icon font can't display in watchfac

Unfortunately, the honestly most likely cause of this (I know, from bitter experience) is a problem with the font file you've built. If you hand edited it, check the .fnt for typos. Check the font PNG image displays how you expect.

And... also check that you are using the correct character for the icon you are looking for.

This one is probably human error on your part, sorry. ;)  

I agree, there is no feasible reason why one icon would work and the other wouldn't, in my opinion. 

Your png is only black and white, correct?