I only clicked once and all patients with id's from P0000002-P0000010 were added.
When you actually click on the button, there is a delay, in which you cannot click on anything else on the page, until which several patients get added. This doesn't happen every single time you click on the button.
I have not tested this on 1.3-milestone-4.
I think this has been fixed, but I've never been able to reproduce it from just one click. I think the problem is that sometimes the browser/OS/mouse driver or whatever wrongfully sends a bunch of clicks instead of just one. Can you test on master if you can still reproduce it?
can it be that some systems are just very slow, and after a click the user may think the click did no go through (since there are no visible changes) and just clicks again (or some windows users tend to double-click even links which are supposed to be single-clicked - would it correctly only create one patient in that case, assuming the page has not reloaded yet between two rapid clicks?)
This is the only way I could reproduce it, furiously click on the mouse before the page reloads. And yes, the fix I just committed does just that, disable the button after the first click so that further clicks are just ignored.