Automatic Alignment in 2.3 different to 2.2

I’ve run into a problem after updating to the stable 2.3 version. Component glyphs built from a base and a diacritic – say Alif with a Hamza above – do not inherit the metrics from the Alif anymore, but always seem to calculate the metrics with the width of the (wider) Hamza. Note that I am using a custom .xml file in which the Alif and the Hamza are duly categorised as ‘letter’ and ‘mark’.
I’ve just downgraded and opened the file and got the expected behaviour, so I suppose the new version might not read the custom .xml file, could that be the problem?

To check if it picked up your XML, you can select it in Font view and choose Edit > Info for Selection (Cmd-Opt-I).

If it’s in the same location, could there be any reason why it’s picked up by one version and not by another?

Whether it’s because of the xml or not, I can definitely confirm that Glyphs 2.3 applies a different (and wrong) advance width to glyphs built from one base component and a mark component, and that opening the file with versopm 2.2 corrects the advance width of the glyphs under concern automatically and without prompt.

Could you send me the .glyphs file and the GlyphData file?