[BUG?] git rebase not accepting :/ syntax

In 1.7.10.3, "git rebase -i :/Merge" will complain with:

fatal: Needed a single revision
invalid upstream :/Merge

... whereas "git rev-parse :/Merge" has no problem resolving
to a single revision.  OTOH, "git rebase -i HEAD^{/Merge}" does
work, and rev-parse resolves it to the same commit.

Is that due in some way to the semantic differences between the two
revspecs, or is that just a bug ?
-- 
Yann Dirson - Bertin Technologies