If I use Glyphs to create accent small capitals with names that begin with uppercase letters, such as Iacute.sc, the sidebearings will be I(number) rather than I.sc(number), with number being the values from I.sc. So they only remain correct until a change is made.
On a related note, there needs to be a preference for turning off Glyphs automatically assigning sidebearing values to other Glyphs when it builds Glyphs from composites. This feature is great when I need it and it works right. But when I don’t need it, or it doesn’t work, I have to manually edit out all these assignments. The application should not make these important workflow decisions for me!
You can select all in Font view and delete them all at once.