When deleting a course, you click the delete button, and then get an "Are you sure" page with a further Delete button and a Cancel button. When you click that further Delete button, the deletion starts, but nothing changes on the page until the deletion has finished - which can take quite a bit of time. 

During that time, you can click the Delete button a second time, which starts a second copy of the deletion process. This can then result in either (a) The first process deleting the course completely but the second one failing because things it wants to delete are no longer there (and it's the result of the second one that the user sees), or (b) the two deletion processes interfering with each other and both failing, leaving the course in a broken state.

It's easy to do this - because the Delete button is still on the page a while after you clicked it, it is easy to think that you must have failed to click it, and hence click it again instinctively.

In order to stop this being possible, the Delete confirmation button needs to be disabled/hidden/etc as soon as it is clicked the first time. It also needs to be visibly different, so the user knows they've clicked it.

Bug seen on version 3.11.11, but have checked Github to confirm no changes to source files between this and 3.11.12.