A) switching font style inside a cluster 
Step to reproduce :-
1.Open OpenOffice.org Writer
2.Switch keyboard to Thai
3.Type the character “ก” (by pressing “d”)
4.Then change font style, e.g. Bold (Ctrl+B)
5.Type the character “ี” (by pressing “u”) which add the vowel mark to the cluster
6.The character “ก” will be displayed twice (see the 1st picture)
7.Then change font style again, e.g. Italic (Ctrl+I)
8.Type the character “่” (by pressing “j”) which add the tone mark to the cluster
9.The character “ก” will be displayed three times (see the 2nd picture)

B) add a non-base character in record change mode
Step to reproduce :-
1.Open OpenOffice.org Writer
2.Type the character “ก” (by pressing “d”)
3.Choose Edit > Changes > Record
4.Type the character “ี” (by pressing “u”) 
5.The character “ก” will be displayed twice (see the 3rd picture)