The Forum Preferences allow me to choose how many Threads per Page and how many Messages per Thread will display, but apparently the only 'choice' which works is the default values of 30 and 30. Any other values breaks the page numbering on the forum front page (threads show as having 5 pages when they actually have 15, and so on). I fought with this page number issue since the 'upgrade' broke it, and it was only by deleting both values and saving the change that I figured out what the defaults were.

If the software can't handle other values, they shouldn't be offered as choices.