Confusing UI behavior when defining a new time signature

1) Define a new time signature
2) Press "Add" at the bottom of the dialog

Expected:

Any kind of feedback indicating that the action succeeded. For example the time signatures section of the palette should expand and show the new item scrolled into view and selected.

Actual:

Seemingly nothing happens. The user retries again and again, clicks the "Add" button in the dialog multiple times, and only after giving up do they notice that a few dozen copies of the new item were added to the palette. The user proceeds to delete the redundant items, and must confirm each single deletion.