Double underscore hack no longer working

I just noticed that the double underscore glyphs don’t work anymore in Version 2.3b (856).

There is a new way of adjusting the side bearings of aligned glyphs. You can add an adjustment value as a metrics key: =+10
I have a look at the double underscores.

Thanks! I tried it, it could be a possible solution, the only problem is that the adjustment value gets added in all the masters. Is there a way to have different values in different masters?

You can add a value for each master as with any other metrics key. Use double equal sign. ==+10

Tried that, it was resetting to only one equal sign. I restarted Glyphs and it seems to work now.