Gas limit issue for sending eth to tenx account


I have started using tenx account for depositing my eth to it. But I encountered a strange situation in which it is known that 21000 is the minimum gas limit for a normal eth transaction. And I found out that the tenx account requires more than 21000 for successful transaction, which is about 33705 gas in order to proceed. Any reason lying behind for this? Why don't it just need 21000 , with simply eth transaction?

Failed one
 https://etherscan.io/tx/0x2289dbe1bc5f1064b5612e22411e31232ab467349504ccfe6d44f2dae285e92d

Successful one
https://etherscan.io/tx/0xa4c081bace109125d424e31aeeba34f958c6b03bfd1a38ae6779c0be5150faef