Recent updates to Piklist have a new setting that allows JS validation to happen client side, but for some reason the classes are different depending on whether this box is checked:

div#piklist_validation_error.notice.piklist-notice.error

or unchecked:

div#piklist_validation_error.notice.piklist-notice.piklist-notice-error

Which results in the css for these not being applied evenly when displaying an error.