Does Extension Kerning affect anchors?

Glyphs
1

I was just playing around with the custom parameter “Use Extension Kerning”. My font exports without any errors whether Extension Kerning is active or not. TTX shows significant differences but I guess that is to be expected if Extension Kerning is used (even though it does not have to be).

Out of curiosity, I opened both exported OTFs in Glyphs to compare them. The kerning is identical in both fonts, which is how it should be, of course.

However, the font that uses extension kerning doesn’t have any anchors at all while the other one does. This seems a bit strange. What do anchors have to do with kerning? It is a real difference in the OTFs, or is it the result of an unusual import behaviour of Glyphs?

My question is: Can I assume that the custom parameter “Use Extension Kerning” does not affect the behaviour of the exported font? (I am aware that some software may not support extension kerning but this is not what I am talking about.) So far, I have been generously adding this CP without checking whether it is really necessary, but the missing anchors on re-import make me wonder.

2

This is most likely a problem with the import.
The “Use Extension Kerning” actually means “Use Extension GPOS”. So the mark feature uses extension lookups, too (and those seem to be omitted when importing). I’ll have a look.