When correcting the deprecation of SubFieldBase (just removed it and added from_db_value, works sort of) all is OK except a new unexpected behavior from QuerySet and values_list.
Prior to this doing values_list(...) on the query set returned something like:
[u'L', u'J', u'L' ] but now it returns [([u'L'],), ([u'J'],), ([u'L'],)]
this is obviously as the to_python returns a list (which is correct), but still, not sure why this ever worked in first place and how this can be changed now (on what level to override this to keep old behavioural).
Secondly the .values_list on a multiselectfield is also open for possible interpretations, should it list values used or combination of values use ;-) but this is my problem...
Edit (by blag): Formatted with GFM