That's where you can help us! Would it be possible to prep a scene in which you encounter this issue in V5->V6 transition? It would help us greatly.
thank you for acknowledging the issue!
As far as prepping a scene - the issue it is not something I have experienced, as far as a "transition" when opening the same scene in v5 vs. v7.
It is simpler than that, actually.
in v5 I can UNTICK the "Visible in masks" option (in the "Advanced" channel of a material) - this will make the material (for example glass), invisible in masks, such as IDmaterial and ZDepth both.
in v7 (and v6, I presume, but I haven't tested) this "Visible in masks" option was removed, and replaced with a "Propegate masks" roll-out menu, where one of the options is "Invisible in masks" (which I assume should be identical to unchecking "Visible in masks") - thsi will make the material invisible in ID passes, but HAS NO EFFECT ON THE ZDEPTH pass..
So, it's clear that there was a change in how the ZDEPTH is handled (as a mask)... hopefully this is indeed a bug.