I came across the following issue with a checkbox field that has the 'Allow keyword synonyms' option active:
When the field's list of choices consists of a single entry whose display value is empty, while the alias value ('synonym') is non-empty, one can select ('tick') the checkbox in the UI as expected. However, as soon as the user refreshes the form or saves the document, the tick mark disappears in the UI, while the correct value (i.e., the alias value) of the checkbox item is still present in the back-end. Effectively, the appearance of the checkbox field in the UI and its back-end value are then out of sync.
I think this is a bug.
Most likely the same bug is present in older versions of Notes as well, although I did not verify this.
P.S.: Why did I choose to have an empty display value? Simply because I had to design a form according to a customer's style guide. The regular appearance of the checkbox field did not fit with that style guide. That's why I had to mimic the checkbox's display value using computed text, while letting the checkbox field itself display the box only, no text.
P.P.S.: An obvious work-around is to let the display value consist of an invisible character, e.g. @Char(9). However, this has a side effect in that an empty space appears in the UI on the right of the checkbox field -- highly undesirable in my case.