When using an iOS device and Safari browser, it is possible for a user to click the "Save and return to course" rapidly. This causes duplicate activities to be created. The button "Save and return to course" is not disabled - allowing user to just hit it in rapid succession.

Using a browser in a computer, the "Save and return to course" button is disabled quickly after the first mouse-click, which stops the rapid clicking of that button.

Replication:
1. Using an iOS device and Safari browser,
2. Create a course and turn edit mode on.
3. Select any activity (ex: assignment)
4. Add a name and then click the "Save and return to course" button rapidly in succession.

RESULT: Once the page reloads, the course content page is displayed showing multiple activities with the same name - as a result of duplication from the clicking of "Save and return to course" button rapidly.

Tested on qa.moodledemo.net.