Hyphen based ligatures don't work in WPF

This is related to the issues people have reported with Visual Studio where ligatures that contain a hyphen, such as -> or <!-- don't work in Visual Studio.

It actually looks like this might be a generic WPF issue, rather than just Visual Studio.

I created a dummy WPF application that simply included a TextBlock, Label and FlowDocumentReader. The TextBlock and Label will display ligatures correctly, apart from those containing hyphens (e.g. ->). Strangely, the FlowDocumentReader works as expected.

I tried to debug the Visual Studio editor, and as best as I could follow, it's not the editor that's doing the work to display ligatures - it comes automagically from WPF and Windows. It looks like the editor is using Windows' native "Line Services" and for some reason, this component is treating the hyphen as a separate character, rather than as part of a run - and so it gets rendered separately, and not converted into a ligature. Hyphenation appears to be disabled in the Visual Studio editor code, and it's definitely disabled in the TextBlock and Label in my dummy application.

I've no idea now what's going wrong, and I strongly suspect this is a WPF/Windows issue and not something that could be fixed in the font, but I'm hoping that we get a nice friendly WPF expert wandering past who can help out.

Could it be something stupid like Windows doesn't recognise "hyphen" in the ligatures?

Anyone got any ideas?

Start by reproducing the dummy WPF application with a TextBlock, Label, and FlowDocumentReader, comparing ligatures such as -> and <!--. Then investigate the contrast between those controls and the Windows Line Services behavior described; done would require identifying a concrete, project-relevant cause or fix rather than only confirming the WPF issue.