When using a text field as an exposed grouped filter with the checkbox to allow multiple selections, I get the following error when trying to use the pager to go to the next page of results:
An illegal choice has been detected. Please contact the site administrator.
This shows up in the watchdog as:
Illegal choice 0 in field_presenter_last_name_value element.
Using Better Exposed Filters with the exposed form in a block.
I've attached screenshots and the display export.