Hi,
I have previously posted in a regular forum about an issue with moving/copying regions on top of frozen tracks. From what I gather, it is a bug.
When you unfreeze any of these tracks, the region you added doesn't stay as it was - instead there's a mess of overlapping media items that I can't make any sense of.
The original post with a little more details is here:
https://forum.cockos.com/showthread.php?t=225322
It's quite a problem, as if you have a project with lots of heavy frozen tracks, it is next to impossible to edit regions.
Cheers