No auto-completion when use RIME halfwidth

When I use RIME (Weasel to be exact) to type Chinese with halfwidth (半角) mode, I type key [ to get a “[” directly, while in this situation auto-completion is not working. If I change rime to English mode or use other input method, auto-completion works.

Relevant config in file symbols.custom.yaml:

    '[' : '['
    ']' : ']'

But, after I remove this two line in symbols.custom.yaml, the behave of key [ doesn’t change, while auto-completion works fine.

Why does this happen? Should I post this in bug-reports?