If the user provides :append and :prepend options to select, the text/HTML will be appended or prepended to the control. If the user provides those options to collection_select or grouped_collection_select, they have no effect. I don't see why this should be inconsistent.

I'm not sure whether this is a bug or a feature request.

At ae08c5b (Feb 15, 2014), specifically ae08c5b#diff-d858d9de5eda99f11a7840b6c015c89eR8 and ae08c5b#diff-d858d9de5eda99f11a7840b6c015c89eR40, the handling of select and collection_select were moved out of the "generic" definition of the bootstrap_form helpers. In doing so, it looks like they both lost :append and :prepend.

It looks like it was fixed for select with PR #327 (Apr 24, 2017), but not for the other select methods.