Layer.coverage() issue

I think there’s an issue with layer.coverage(). When I run it on a few layers, everything seems fine, but when I try to execute it for all layers of a master, I get an infinite loading spinner.

I suspect that the output value for italic layers is incorrect. I get a 98% coverage with Roman layers but only 80% with Italic ones.

To get same coverage value in Italic, I need to fill extra space :

I’ll have a look.