User reports that fonts are different heights when rendering at 75 dpi (instead of default 72) as well as some nearby values such as 73-76. This was reported using the x11alpha driver, but I have reproduced with png16m as well. Sample files plus screenshots attached.
Created attachment 584 [details] gs-test.tar.gz
Created attachment 586 [details] y.bmp Attaching a draft about grid-fitting the character y at 72 dpi with no antialiasing. The pole 4 is the right upper corner. The next pole 5 has an Y coordinate greater than the Y coordinate of the pole 4, and the difference is 2 times greater than BlueFuzz. Therefore the segment doesn't recognize as a horizontal one, and the horizontal alignment zone isn't applicable. The failed condition is gxhintn.c (in rev.1.44) ln 1571. IMO the font is buggy. We could work around with increasing the threshold, but not sure that we should. With GS_7_0X same problem happens at different resolutions.
Oops, in the comment #2 I've meant 75 dpi.
Fixed with gxhintn.c 1.45.