I'm taking a guess here... have not tested or verified myself...
BUT... check to assure that "apply edits to all members" is checked on...
I filed an IR for exactly this (in an alternate positions asm)
This asm had the Undo button disabled, didn't know why.
Then I noticed it was an Alternate Positions assembly. To rule that out I did some checks.
Populate a member > member has Undo enabled
Convert back to Alternate Positions > Undo disabled.
I do not see why this was logged as a PR – it explicitly states in the Solid Edge help that Undo is *not*supported in Alternate Assemblies:
Thanks for clearing that up, I didn't know about the Undo-restriction.
PR'ing the IR however was a GTAC decision after uploading the files. I think GTAC missed the fact that it was an Alternate ASM. I believe the PR is still open.
Oh trust me, I realise that if this is a PR it made it through GTAC :-(
As to the status of your PR, already closed, unsurprisingly, as "working as designed" :-)