Whispering doesn't work across servers

So, yesterday i met someone in pubs, he had to go cw and we kept whispering
Whoever, it stopped working as soon as he changed to UK Clan server
I changed from UK2 to UK5, still couldnt pm him, changed to NA, same effect, then went to the same server as his and it worked.
Today i tested this with a friend , he was on UK3, i went to dif servers, couldnt message him.
Then as i changed to his, i was now able to whisper once again.
Is this just happening to me? If not, can we get a fix?