Before version 1.49.3 the pango was using (probably) values from BLC table, since 1.49.3 pango uses harfbuzz for metrics and it seems harfbuzz is using OS2 table. Result is font with 1px extra for ascend/descent.
Solution seems to be to use FONT_UNITS_FLOOR instead of FONT_UNITS_CEIL when storing file.
Fixes: #7