This is the situation.
I tried leveling my account B in Janeway so I decided to borrow my equipment from my account A. The trade was successful. After some time I've reached 99 with my character in account B so I did a trade again to return my equipment to account A but....
It was so laggy. So horrible that I couldn't move my mouse pointer to the item and drag it to the trade box.
So I thought that maybe if I switched client it will go smoothly. I logged out on my account A and logged my account B on that client and vice-versa but still no hope.
Then I tested again, opening an account C and doing a trade with account B. It went smooth with minimal lag.
Is there a rule in the system that does this or it was just purely coincidence?