When editing tiled sprites and 9-patch objects via piskel, and maybe every object which only requires you one frame, piskel is forced to enter a strange “single-frame” mode which limits the canva to a single frame and you have to work on that.
Normally, I open a separated piskel window and work there, then copy it back to the original window.
My suggestion is to make it avaliable to add frames, and display a message when opening piskel via tiled sprite/9-patch:
“Warning: upon saving, only the first frame will be used and the rest will be discarted.”
But why would I want to be able to work in multiple frames even tho only one will be saved?
Its because since in piskel there is a issue with undo crashes, duplicating the frames is a workaround to avoid that.
Duplicating the frames can also be used make a backup before making a big change in the image.
So consider those to make multi-frame mode avaliable in piskel for single-image objects just like when editing sprite objects.