Email me when this thread has replies.

Can someone with me with next problem:
Whenever i check the option "Email me when this thread has replies", somethings will go very wrong. Even u will not get any error message.
Because when u opens that thread again, you will see it's uncheck again. If u try to re-check it then u will get duplicate kay problem in de database.
But the most important problem is that u can't make any new thread in the forum anymore! You will get some critical errors.
If u have luck with the "Back" button from the bowser you may un-check this option to resolve this "New thread" problem.
I can reproduce this even on this forum.

Is this a known issue? Anyone know how to fix this problem?

Thanks in advance.

Of course. You can reproduce the critical errors and broken "Add thread" function by following steps:

1. Go to a thread  which u don't have subscribed  any notification. Then u will be able to subscribe notification with checkbox "Email me when this thread has replies".

2. After that, just simple try to add a new thread to the forum. Then you will not be able to make new thread anymore. You will get some critical errors.

Remarks:
- When u reopen the same thread u will see the checkbox is still uncheck. But when u try subscribe again, then you will get duplicated key in forum_tracked table.
- If you delete that thread, u can make new thread again. 

PS. Chris, thank you for all your effect to make this nice new release.

Thank you.

Is it possible that i can disable that checkbox somewhere in the code now? 
Lot of our users have this problem now and our helpdesk is going crazy at this moment.