Have had this happen thrice now, and just noted at what point it occurs.
Have three longish regions into which I've dropped track ID's. Total time is too long for a single disc, so pick a chopping point. Upon making the edit, track ID's in that region upstream of the slice disappear except for the ID at the head of that region.
OS 10.5.8; WM v. 1.6.1
Looks to me as if the workaround would be to shorten the program prior to adding track ID's, but that is not my preferred method. I can't find anything in prefs that enables/disables this "feature".
What am I missing? (Be kind...)