problem 1:
I have an SHP (lets call it A) with 442 frames (black & white frames start from frame 222)
If i do Edit > Insert Frame it will add the new frame after frame 441 instead of after 442. And I will have a total of 444 frames.


problem 2:
If I do Mass Frame Operations > Copy Frames
from another SHP (lets call it B), from 341 to 619 into SHP A
in frame 443 (to not overwrite frame 442) then the result in SHP A is:
SHP A now has a total of 721 frames.
222 to 360 will have empty frames.
361 to 442 will be some of the black & white frames of SHP A.
BUT from 443 to 581 the black & white frames will be overlapping with frames from SHP B.
582 to 704 will have only the shadows of the black & white frames overlap with frames from SHP B.

Update: I understood how it works (not user friendly) and fixed it.