Thanks for the quick responses.
I've managed to render text correctly now using LCD filtering (the new 2.8.1 version). I was able to do it by ignoring the glyph metrics and using the bitmap size itself. This works well enough for now, and the text looks great, but I would like to be able to retrieve final dimensions of the bitmap without actually rendering/allocating anything, so I can calculate the layout of a bitmap-font/texture-atlas, and blit the glyphs afterward. I've been doing this for while and only ran into a problem when I tried the new LCD filtering.
I understand why the padding would be needed, but why wouldn't it be included in the glyph metrics (width/height)?