Slots selector unavailable when capacity is unlimited

As far as I can tell, the "Slots" selector on the UI in unavailable when the node capacity is 0 (or unlimited). I am not sure whether this is a bug or by design, but I do need registrants to be able to select a number of slots for every registration, whether the capacity is 10, 100, or unlimited.

I tried this both with the capacity being drawn from a node field and with it being the native Node Registration field. Same result in both cases.

As a workaround I could set the capacity to some arbitrary high number and let that be how we manage unlimited capacity, but that seems awful.