I've run into a problem with GSUB coverage offset overflow errors in a largish font I have been working on. Adding useExtension to various lookups solves the problem when generating the font in FLS 5.0.4, but not in 5.1 where the error remains. Moreover, attempting to compile directly using AFDKO also fails, so I suspect that there is a bug in AFDKO 2.5 which is somehow causing the useExtension directive to be ignored.
I was wondering if anyone has successfully compiled code using this directive either in AFDKO 2.5 (or FLS 5.1 which relies on AFDKO 2.5). This would help me determine whether this is indeed the root of the problem or whether there is some other less obvious problem with my code which FLS 5.0.4 (ADFKO 1.6) accepts but which FLS 5.1 (AFDKO 2.5) does not.
(n.b. by 'successfully compiled' I mean compiled where the directive is actually necessary to prevent overflows -- not just where it is present).