How to reproduce:

start OOo for the first time, so the 'first start wizard' comes up
- start it like the testtool does it: 
soffice.bin -enableautomation -norestore -nolockcheck -autocrashreport
-accept="socket,host=localhost,port=12480;urp" -writer

click through the wizard, after pressing the finish button only the startup
screen is shown and stays there forever.

If I would start without -accept="socket,host=localhost,port=12480;urp"
it would work and not freeze, but this parameter is needed.

Workaround is to start OOo the first time manually and click through wizard.
After that testtool is able to start and handle OOo.