Thank you very much indeed!
I was quite a bit upset with 5.7.2 mostly for a reason have not seen mentioned: they broke the dictionary handling in it.
On versions <5.7.x, if Kindle could not find a word in the default dictionary, it chose Wikipedia
only after there was no hit in the other installed dictionaries either! But on 5.7.x, it
goes straight to Wikipedia when there's no hit in the default one...

(and as our English-Hungarian dictionary is much less thorough than the Oxford English-English, it often happens. So on 5.7.x, every time you have to swipe from Wikipedia to dictionaries, select Oxford, check the word, and finally select EN-HU again: very inconvenient)
Now I've downgraded to v5.4.5.1 on my PW2 2GB, everything went fine, and dictionary works again as it did before!
(though I'll probaly upgrade to 5.6.x because of Bookerly)