I didn't realise that happened-I thought if a conditional order...

I didn't realise that happened-I thought if a conditional order was time stamped at 4.5 it would go to the end of the 4.5 queue. I had a similar query I was going to ask-I was actually topping up at 4.4 about the same time Greedy was selling. About 20 000 out of my 200 000 order got filled-the price then went to 4.5. I then noticed the price had gone back down to 4.4 (a trade of 25 000) but none of these were my order, even though I was top of the queue?? Also what does XT next to trades mean?

Looking forward to next week!!