Neil,
You are right, it was Verdana 
(I wonder how the stc know it should use this face)
"font smoothing" seems to have no influence
I played with font names, smoothing, wxSTC_P_WORD style ("import")...
Just to summarize the situation.
If you prepare your stc styling like this:
self.StyleSetSpec(wxSTC_STYLE_DEFAULT, "what_you_want")
self.StyleClearAll()
other styles
everything is working fine, but with
self.StyleClearAll()
self.StyleSetSpec(wxSTC_STYLE_DEFAULT, "what_you_want")
other styles
you go into troubles.
Jean-Michel Fauth, Switzerland