Here's another one. On Firefox. I was fishing... got a fish. I clicked the reel in icon and waited for about 2 seconds (my FF was kind of laggy), saw that nothing happened and went with the mouse cursor over the white image on the button, then clicked again. This time, the button highlighted as if it was really pressed.

The "keep"/"drop" screen appeared, as in the screenshot below, but unfortunately the buttons were inoperable, since "An unknown error occurred: already_reeling".

I think that once you clicked on the reel in button, this event should somehow lock the button from subsequent clicks in the case when the browser or the Internet connection is slow and doesn't update the 'fish bit' GIF into the 'reeling in' one.

It does. It hides the button

Well... apparently it hides the button in most cases, but not all.

When the page loads slowly though - that's how I caught this error, if the connection and the browser would have worked at normal params, this wouldn't have occurred - there is a chance that the reel in button will not record the event of being pressed until after it throws away that error.

That is, to say, your 'already_reeling' mutex is slightly defective

I suspect that it's simple to fix and arises almost always as a result of a weird connection delay or misclick. I will try to lock out buttons upon receiving the click event.

Yep, it's definitely something not easy to spot. Thanks for looking into the problem. (So I guess Internet connection ups and downs can be useful sometimes.)