History/origin of the pronunciation/spelling of "Butcher"?
Solution 1:
There are a number of words in which a 'u' is pronounced /ʊ/ even in dialects (such as South Eastern English) where it is normally /ʌ/. They all or nearly all have a labial consonant preceding it:
Eg: Pull, push, put, puss, bull, bush, full.
This is not a reliable environment: consider puck, buck, pus, putt, which have /ʌ/ in such dialects.
So there is nothing anomalous about "butcher": it belongs to an established class of words with /ʊ/