The root cause was some code that tries to omit keying loc, rot, or
scale based on the current transform mode and pivot type. The idea is
sound, but for it to work properly it also needs to know if more than
one object is being transformed or not. Notably, this bug affected the
scale transform mode as well, not just the rotation transform mode as
reported in #123961.
This fixes the issue by passing a flag down that informs that code
whether more than one object is being transformed, and using that flag
to correctly omit loc/rot/scale when possible.
PR #123998
Pull Request: https://projects.blender.org/blender/blender/pulls/123998
953b319ea8