dabbrev-upcase-means-case-search

dabbrev-upcase-means-case-search is a variable defined in `dabbrev.el'.
Its value is

nil

Documentation:
The significance of an uppercase character in an abbreviation.
A nil value means case fold search when searching for possible expansions;
non-nil means case sensitive search.

This variable has an effect only when the value of
`dabbrev-case-fold-search' says to ignore case.

You can customize this variable.