I've noticed a very common mistake that surfaces when people say Birchas HaMitzvos out loud. Instead of saying אשר קִדְשָנוּ במצותיו (kee-di-shu-noo) as written in all Siddurim, many people pronounce it "קְדִשָנוּ" (ki-dee-shu-noo) instead. Is there any source or reason for this change, or is it simply a widespread mistake?
See grammar and pronunciation rules from Jewish Virtual Library. From my understanding of the rules, the correct pronunciation should be "keed-di-sha'-nu". Since there is a dot in the daled, it is considered as if it is doubled, i.e. - ending the 1st syllable and starting the 2nd one, as well.
Offhand, I would say that sounding the 2nd syllable with a chirik has no grammatical basis, as that's not the conjugation of the verb "kadesh" in the present plural in Hebrew. Someone who does pronounce it this way, could be mistaken for using another verb which sounds like he's saying "ki-di-shay'-nu", which would be using a different verb "deshen" meaning "refine", as in the term we use in Shabbat musaf, "am medushnei oneg".