Tested your now in-sync VOB with titles and transitions and it stayed locked.
Under OPTIONS|EDITING tab, choose "Ask: in the Video Transition box.
Then, when a transition between clips does not have sufficient video to cover the trans duration it will prompt whether to Overlap or Freeze.
If Overlap is chosen, the audio may go out of sync if it isn't linked to video for that clip, because video will be moved (overlapped).
Let's take a look at your project - it's the best way to diagnose these issues.
Here's how... http://nch.invisionzone.com/topic/23659-tips-for-getting-help-on-this-forum/
If it contains sensitive material you can link it in a personal message (PM) to me, via the envelope above. Be sure to FILE|SAVE PORTABLE PROJECT AS, not simply SAVE PROJECT, and don't forget to share it.