Can't flip selection in alpha channels

[GazzaBrad]

I've just come across a bug in the alpha channels in the latest 26.2 Beta. 
I'm trying to flip a selection in an alpha channel but the Transform menu item isn't available and greyed out. I've included two screenshots comparing the same action in 26.2 Beta compared to the current 26.1 release.

[GazzaBrad]

Update on this. I've copied and pasted the alpha into a new file in Beta and that works, strangely enough, so it's something in my file. I'm still investigating.

[GazzaBrad · Accepted solution]

OK, my error. It's as simple as I needed to have a layer selected before the transform in alpha was available to flip.
Apologies it's not a bug, I should have checked before posting.