I regularly hit this issue where I type repo:sourc, C-n to select github.com/sourcegraph/sourcegraph, Enter to accept the completion, then Enter to run the search. However, rather than submitting the search, sometimes the second Enter inserts a lang: filter instead.

Sometimes, after accepting the completion with Enter, lang: is selected and sometimes it is not (see two screenshots below). I have not been able to establish a pattern of why it is sometimes selected.