When I install a new font, or even just put a bogus file in a font
directory, all text increases in size.  This effect lasts until the end
of the X session; subsequent font installations have no apparent effect
(I guess the size gets re-changed to the same value).

For example, a full-screen terminal with size 16 Consolas:
[~]$ stty -a
[...]; rows 48; columns 126; [...]
[~]# touch /usr/local/share/fonts/foo.ttf
[~]$ stty -a
[...]; rows 43; columns 105; [...]