They obviously dumped loads of BTC and are slowly buying them back. On the 1st of October, just before the migration started, since there was no warning on Mintpal's website that it was about to go offline, I deposited 0.04 BTC to address 1HkiegCTHNFksNhfHxH4ffLEuq61odrCBg. The deposit went through normally (txid 9cfbf3dd042b63968480214c56d8971cf35bde55cb765976bb7f9f5e2786b68a). Now that the site is back online, my BTC balance is showing only about half that amount, 0.02056931 BTC.

Now the interesting part - look what happened to the BTC on the address I deposited to. One hour after the deposit, the whole 0.04 BTC were transferred to 2 other addresses:

https://blockchain.info/address/1HkiegCTHNFksNhfHxH4ffLEuq61odrCBg

Why the hell couldn't they migrate the address that was already associated to my account and instead moved its balance to other addresses? That looks extremely suspicious to me.