Declension class fi:solakka

I noticed that we have always had the illative plural wrong in declension class "solakka", in the sense that the form with one "k" is the more common one and should thus come first. See e.g. puolukka: puolukkoihin" is above "puolukoihin" and it should be the other way round. It seems that KOTUS's net dictionary has it wrong. If you google any word in this declension class, you'll mostly get at least hundred times as many hits for double-k-form than for the single-k-form. For once, I want to disagree with KOTUS!

I wrote it the wrong way. Should read: If you google any word in this declension class, you'll mostly get at least hundred times as many hits for single-k-form than for the double-k-form.

It's strange, because normally the illative plural has the strong grade doesn't it? I wonder why there's this exception. Anyway, I've swapped the forms around. Should the same be done for the laatikko class?

Indeed it seems that also in "laatikko" class the single-k is more popular. Here are numbers from Google searches: laatikoiden 114 000, laatikkojen 9 800, laatikoitten 3 600; laatikoita 242 000, laatikkoja 10 000; laatikoihin 78 000, laatikkoihin 6 600; laatikoina 10 000, laatikkoina 3 400; laatikoineen, laatikkoineen. If one chooses another word, one gets different result. With "valikko" the frequencies are more even (ratio is btw. 1 and 2), and in comitative the double-k form is more frequent.

Forgot laatikoineen 8 000, laatikkoineen 4 000. Also in "puolukka", puolukoineen is much more popular than puolukkoineen.

I wrote KOTUS about this. Their comment: good observation, but we cannot change the system right now. I take this as support.

For the record, the historical background is that coda *j used to trigger gradation of geminate stops in some Finnish dialects (IIRC there's no evidence for gradation of singletons), but it's been mostly analogized away from existence; in particular since plural & past tense *-j has often contracted with the preceding vowel to -i-. (This has included even *oi-stem nouns such as > dial. kukoi for kukko.) However, -kka always takes the plural stem -kkoi-, so gradation to -koi- had pretty good odds for remaining.