[[boa#Finnish|boa]]
Here's a related bug I just noticed. The declension module for Proto-Finnic seems to go wrong with creating past/imperfect stems for A-stem roots with U-diphthongs. They should be determined by the stressed vowel, not by the *-u-. Thus roots with a back illabial+u diphthong, i.e. *CauCa-, *CeuCa, *CiuCa currently show *-ei- (see e.g. Lua error in Module:parameters at line 95: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E., Lua error in Module:parameters at line 95: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E.), though they should have *-oi-.
For further reference, we're eventually going to need toggleability for this anyway, since there is a small number of word roots that have *-oi- despite a preceding labial vowel. The clearest is Lua error in Module:parameters at line 95: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E., plural stem Lua error in Module:parameters at line 95: Parameter 1 should be a valid language or etymology language code; the value "fiu-fin-pro" is not valid. See WT:LOL and WT:LOL/E.; compare suola, sool.