I can see this being possible if one had booked the same night in two different hotels. (an existing stay that can't be cancelled or is part of a special rate so left as is, then needing to be in a second hotel but not getting the stay credit for it as already in another hotel...for example.

Might simply be a mistake but I've definitely 'been' in more than one hotel on a particular night for one reason or another...I now try to make sure it is at least a different chain so as to get credit for them but not always desirable or possible,