Can't confirm that.

@dcarter_za:
Please
- specify your OS and Platform
- tell us your exact OOo version (localization, source, build, ...)
- attach a sample file
- contribute screenshots comparing tooltips of OOo documents and others in 
  the folder

Created attachment 54750 [details]
Screenshot - Openoffice document tooltip

Created attachment 54751 [details]
Screenshot - Plain text document tooltip

System settings:
- Windows XP running on a PC, SP3
- Windows XP Regional setting set to English (South Africa), with short date
format set to d/M/yyyy.
- OpenOffice Version 2.4.0
- OpenOffice Locale Setting: English (UK)

See screenshots showing tooltips on an OpenOffice document, compared with a text
file. Both test files are attached.

Created attachment 54753 [details]
Sample OpenOffice document used in screenshot

Created attachment 54754 [details]
Sample plain text document used in screenshot

I checked with "2.4.1  Multilingual version German UI WIN XP:
[680m17(Build9310)]"  and can NOT confirm the reported effect. I did several
experiments with the WIN settings, but tooltip-view was always correct. Also
with "New OpenDocument Text.odt" and my own 2.4.0 documents not reproducible.

Problem occurs on my installation of Windows XP. Running the command "Winver" shows:
Version 5.1 (Build 2600.xpsp.080413-2111 : Service Pack 3).

This is not a new problem with SP3 or the current version of OOo - I had noticed
it over the past couple of years.

@dcarter_za:
Any new ideas / results?

I have done some further testes and found that files created with more recent 
versions of OO show the file date in ISO format, but files that were created with 
older versions show the date in the incorrect format. See attached examples, using 
OO 3.1.0 build 9399. I don't know what version of OO I had used to create the 
older file but it would have been the version that was current at that time. In 
the examples you can see the modification date shown in Windows Explorer in the 
format d/m/yyyy but the tooltip for the older file shows the date in m/d/yyyy 
format.

Created attachment 63666 [details]
Example 1: In older file, format of date in tooltip is m/d/yyyy while system setting is d/m/yyyy

Created attachment 63667 [details]
Example 2: In newer file, format of date in tooltip is ISO format

Differences in file timestamps can be explained by my changes in timezones. My 
date and time formats, however, have not changed.

Attachment 54753 [details] tooltip shows 26/06/2008 while Region and Language Short date is M/d/yyyy
AOO410m1(Build:9750)  -  Rev. 1562493
Rev.1562493
Win 7

CONFIRMED means that there is a real bug what has to be fixed for AOO and where all relevant information a normal user can contribute has been contributed. So here I disagree with status CONFIRMED:

(a) Due to Edwin's research that there exist documents (like reporter's 
    sample document) what have been created with a very obsolete OOo version 
    OpenOffice.org/2.4 (due to meta.xml) what makes WIN Files Explorer Tooltip
    showing date with transposed D<->M. We can't repair the fact that those 
    documents do exist.
(b) we can't even know whether it's a WIN bug
(c) I can't see any relation to current versions. So back to UNCONFIRMED
(d) Modify summary due to Edwin's result (Also WIN tooltips)
(e) The problem is really limited to Tooltip, Files-Explorer -> Context menu -> 
    Details shows date correctly?
(f) Due to Comment 10 The problem seems to be FIXED?
(g) We should check whether AOO 4 repairs midification date so that edited 
    document shows correct tooltip.

@Edwin Sharp
Can you tell any relation of your AOO410m1(Build:9750) to the WIN file Explorer Tooltip? I think you did that selection for "Latest Confirmation on" accidentally.
Can you please do a test concerning (g)? I can't reproduce on my PC

@dcarter_za
The problem has definitively gone with current AOO versions?
Can you also do a test concerning (g)?

Created attachment 82804 [details]
tooltip vs. Win 7 Region and Language

AOO410m14(Build:9760)  -  Rev. 1573601
2014-03-03 17:47:48 (Mo, 03 Mrz 2014)

See comment 16

We need a way how to reproduce the problem, screenshot 2014-03-06 does not tell anything concerning a AOO problem. Of course it is strange that tooltip dd/mm are interchanged compared to OS settings. But who can know whether that is not  a WIN problem?

@Edwin:
Can you please compare a AOO document and a not AOO document, both created newly today, tell all details how created and and and so that we can reproduce the problem that AOO documents show date wrong in WIN tooltip while other documents show  date correct in WIN tooltip

Created attachment 82805 [details]
tooltip2 vs. Win 7 Region and Language

see comment 19

Edwin Sharp:
Original report is concerning problem "... tooltip shows the modified date in the format M/d/yyyy even if the regional setting for Windows is set to display a different date format (e.g. d/M/yyyy)"

Your WIN explorer tooltip of document 91067.ods does not show a short date with shashes in tooltip, but an ISO format date long date in toooltip.  So it can't confirm the reported problem.

We can discuss whether it's appropriate that WIN explorer shows a long ISO format date for AOO document (Have you any WIN specification concerning date format in Toolitps?), but that's something completely different from the original report.

This issue is somewhere between irreproducible and fixed, but definitively not confirmed.

Before you modify status to CONFIRMED, please contribute a clear, well sounded reasoning why your conclusion is that we have an AOO bug here. Your latest screenshots do not show any problem with AOO.

The problem of original report does no longer exist due to Comment 10 and others, so FIXED.

Concerning Edwin's observations in Comment 19 I submitted new "Bug 124380 - WIN Files Explorer in document tooltip shows date of modification as ISO 8601 instead of OS setting date format". I am tending to see that as intended behavior / feature, but it's indeed a little worrying.

Created attachment 82820 [details]
tooltips in Win XP AOO 4.1 beta