Weird behavior of Hebrew composing marks

I’ve tried my hand at Hebrew for my latest typeface, and although I have no experience whatsoever with that script, the information on Wikipedia and in Glyphs seemed rather straightforward to me (as far as I can tell).

However, something seems to be going seriously wrong with the Nikkud the Italic. I’ve set up the anchor points so as to make sense in Glyphs:

…but this is what I end up seeing in Pablo’s font testing page:

Very annoying! It seems to work reasonably well in the upright cuts.

Can you send me the font?

There was a bug in one version of Glyphs that caused this behavior in uninterpolated instances. Is fixed in latest betas.

The cutting-edge version I have still causes the problem. I’m sending you the file.