SUMMARY
When adding a frame in the animation curves docker before the first existing frame, the parameters of the new frame are set to default values (1 and 0 for scale and everything else respectively), but the canvas doesn't reflect that until the user switches to another frame and back.
NB: not to be confused with bug 478448, which has the exact same steps to reproduce but is a different bug on master.

STEPS TO REPRODUCE
1. Create a non-empty paint layer, add a transform mask to it. Select the mask.
2. In the animation curves docker add a frame to it at t = A, A >= 1.
3. Using the transform tool, make a change to the mask at A, e.g. a rotation.
4. Add a frame at t = B, B < A.

OBSERVED RESULT
At B the layer appears to have the same transformation as at A. Switching to another frame (time) and back to B makes it correctly appear as having the the empty (identity) transform.

EXPECTED RESULT
Creating the frame at B makes it immediately appear as it would without the transform mask.

SOFTWARE/OS VERSIONS
Linux: Ubuntu 22.04
Qt Version: 5.15.7
Appimage

ADDITIONAL INFORMATION
This appeared in 5.2.0, regression compared to 5.1.5.
Present in 5.2 as of krita-5.2.2-24c985bda8