This bug is from Chosen jQuery plugin:
https://github.com/harvesthq/chosen/issues/92

Chosen module may add a workaround for this issue, or just keep this bug report open while Chosen jQuery plugin is fixed so Drupal users can find this info quickly.

Comments

Assigned:Unassigned» Cyclodex
Status:Active» Needs review

Can you retest this with the latest dev version. Should work now, as it works for group field I think it should also work if it is hidden.

I have tested it, and it still not working if it is initially hidden ..

Status:Needs review» Active

Changing to "active" because of #2 info.

Status:Active» Closed (duplicate)

As far as I can tell, this is an duplicate of #1491002: Doesn't work in collapsed fieldset and should be fixed with the min-width defined in the config.