Mark Pilgrim says it pretty well in WrongRoom: “you’re writing a text editor. Stop doing that. It’s 2007.”
Q: Why is there more than one text editor?
A: Because they all suck.
So after struggling with SWT’s StyledText for a while, I’m back with jEdit.
jEdit has its own flaws, though. The text renderer is … basic. No unit tests. But it seems the developers are more approachable than the Eclipse guys. So maybe it will be less effort to add the missing features.