I think that’s needed, for example, for French, where it’s common to have a space before the colon. Usually, in English, there is no autocomplete because there is a letter before the colon.
“Testing:” doesn’t trigger autocomplete but
“testing :” does, and to prevent that, you can configure that at least one more character needs to be entered to trigger the autocomplete.
I don’t think it should be necessary to use this setting for this bug.
The description is ambiguous but I think that’s for after the colon… we already don’t trigger the popup if there’s a letter (word?) character before the colon: