I tried the examples/customrender.pl program with gtk 2.12.11 and
perl-gtk 1.202 or the cvs and got just a horizontal line when clicking
to edit in the custom renderer. Screenshot below, the line is on the
left.
I suspect the line is the TextView with height 4 pixels, and that that
height may be all its requisition asks for. Did it used to ask to be a
size which would fit its text, or something? Or is the viewer/cell-edit
stuff meant to stretch it to the cell size anyway? Forcing the latter
seems to work, but is that supposed to be necessary?