Poloniex have a fee to deposit funds? I sent 1000 (+1 fee) Ardor from my cold wallet, but poloniex deposit only 998 Ardor

This a poloniex bug?
It is possible that you actually sent 1000-1=999 to Poloniex, and then they sent 999-1=998 to their cold wallet.
What is the logic behind that? Why would they deduct coins from a customer's deposit if they want to send part of their holdings to their cold wallet? I have never had that before. Only fee that should be deducted is the tx fee on your side when you send it, but nothing more.