Single on/off checkbox doesn't work to check if field is empty

Hello,

I'm having trouble getting a single on/off checkbox to work with a field that I want to filter. I'd like to filter a standard text field and, if the single checkbox is checked, the results are filtered to only show items with content in that text field.

Current settings:
Filter criterion: Single filter - "is not empty (NOT NULL)"
Exposed filter settings: Single on/off checkbox

When I check the box and press the button, however, the checkbox becomes unchecked and no filtering occurs. Is there a better way for me to filter (with a single checkbox) whether or not a field is filled in, or is this a bug?

Thanks!