Cudatext (gtk2 and qt have have this problem):

Geany editor for a counter-example, text looks exactly the same, but no cut-off:

I have a progress, now it is

beta updated in /c. please test?
Works great now, thanks
Minor issue with this beta - with 'spacing_y=-2' first line gets cut of a bit at the top:

good catch. thanks. beta updated, pls see.
changes, updated the beta again now.
Line backgrounds now look weird at the end of lines:

And current line is not highlighted at all, checked that PROP_HILITE_CUR_LINE=True
Fixed both! putting beta to /c in 5 minutes. pls test again.
All is fixed, thanks
Most helpful comment
I have a progress, now it is
