Glyphs 4.1.1 (4108), reinterpolating the italic intermediate layer of a produces an upright outline. The same operation works correctly in Glyphs 3.
The font has Weight and Italic axes, with four masters:
-
Regular:
[90, 0] -
Regular Italic:
[90, 12] -
Heavy:
[266, 0] -
Heavy Italic:
[266, 12]
The glyph has intermediate layers at [168, 0] and [168, 12]. The italic intermediate is correctly associated with Regular Italic.
I can send you the glyphs file to check and reproduce.