The pronunciation of the first syllable of butcher as /ˈbʊt͡ʃ ..../ is for non-native speakers astonishing. From spelling alone, one would probably guess that it's pronunciation would be more like that of "but" /bʌt/. Surely there must be historic reasons for this (guessing sound-shifts, time of borrowing from french, etc.). What are the reasons for butcher being pronounced the way it is today?
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/