Võta heaks!
jahimees wrote:PS Käänemine on 'declension', eks ole?
Yes, indeed.
Another question connected to the phenomenon of overlongness: are diphthongs always overlong?
No, for example 'koera' (genitive - long) vs. 'koera' (partitive - overlong), just like regular double vowels are not always overlong: 'hoone' (nominative - long) vs. 'hoone' (genitive - overlong).
And what about a situation when there is p, t or k followed by a diphthong? Does p, t or k become overlong?
Wait... did you mean 'k', 'p' or 't' is in front of a diphthong ('kaun') or after ('auk')?
In the first case it depends on what comes before 'k', 'p' or 't', in the second case (diphthong + 'k', 'p' or 't') - I'm not sure... I would have said that for example 'väike' is not overlong, but according to ÕS it should be - I'm confused now, I have never pronounced it overlong.
I guess you are right then, that diphthong + 'k', 'p' or 't' always make up an overlong syllable.
Does not distinguishing between long and overlong vowel/consonant variants of the phonems cause problems with understanding in everyday situations?
I guess it could, but I haven't had very many conversations with non-natives in Estonian, so I haven't experienced that.
Are there any Estonian dialects that don't have such a distinction?
I don't know. I haven't noticed the lack of it in South Estonian languages - but on the other hand, I haven't listened to them very much either. Maybe North-East Estonian, which should be more Finnish like, if I remember correctly - if it still exists, of course.
Haven't heard it myself, though.