With the change to use "start-here" to grab icons, you can no longer use non-square icons.

[Maxweill]

It used to be the case that the custom icon you pointed to could be of any size, and the bar would render it:

Now, however, 'start-here' icons are scaled to be a square, and so this no longer works.

[radasbona]

I have the same theme (and problem)