I've found a temporary way of accepting new realms and configuring your realm for anyone interested.
You need to have access to at least one more computer than the the one with problem. You install Minecraft on that second computer and from there you will probably, (as long as that computer doesn't have the same issue,) be able to accept invites, configure your realm and leave other people's realms. From the first computer, (the one which is experiencing the bug,) you should now be able to play on the ones you have accepted from the second computer.
Note: This does NOT solve the problem. You can still not accept, reject, leave or configure the realms from the first computer.
Olle Molin
I've found a temporary way of accepting new realms and configuring your realm for anyone interested.
You need to have access to at least one more computer than the the one with problem. You install Minecraft on that second computer and from there you will probably, (as long as that computer doesn't have the same issue,) be able to accept invites, configure your realm and leave other people's realms. From the first computer, (the one which is experiencing the bug,) you should now be able to play on the ones you have accepted from the second computer.
Note: This does NOT solve the problem. You can still not accept, reject, leave or configure the realms from the first computer.