I updated this morning to the suggested version (1.6.5)
The bug: I was reviewing my last changes through SourceTree, then I went back to my editor (Eclipse) to change another small thing. Swapped back to SourceTree which updated itself with the change I made. At this point I right clicked on the file entry (in the unstaged area) that I wanted to commit and hit 'commit'.
After this click the client crashed.
I could reproduce easily this crash just by reopening the client and directly right click on the file to commit.