i'll just tell you what happened in my case (don't want to make a ticket)
- client was very slow.
- i traded with friend n1.
- shortly after or at about the same time friend n5 traded with me
- i declined his trade since i had traded with friend n1.
- friend n5 tried to trade with friend n1, however friend n1 was unable to accept. nothing showed on his screen, and he was locked in doing anything. he couldn't choose his summoner spells either.
that's all i got, hope you guys will manage to fix it.
Thanks for the details. Let's see if we can reproduce with those instructions.