When value in checkbox is modified twice in a row (so it is at its original value) an 'undo' button is still visible even when it shouldn't be.

Cause:
IPA server sends boolean values as 'TRUE' or 'FALSE' (strings). Checkbox_widget converts them to JavaScript boolean (true, false). Save method in checkbox_widget is returning array with a boolean. So test_dirty method always evaluates to dirty because 'FALSE' != false.

Probably not a regression - was in 2.1.2 maybe earlier.