[Gimp-developer] Bug? Clone Tool after Merge Layers

[Brendan]

Am I doing something wrong or is this a bug?

Action:

Have two layers, one has a Layer Mask that I have painted in to unmask the 
edges of a models face from a Gaussian Blur tool.

Layer Mask gets squashed down with a "Merge Visible Layers" command.
After that, I can't seem to get the Clone or Heal or really any drawing tool 
to work on the image. Unselected everything even.

Seems non-obvious to me, so if it's not a bug, there needs to be an error 
message at least....