Do not worry.  That is correct behavior.

Every time you spend Bitcoins all the Bitcoins from the source address are used and the address is thrown away.  Kind of like spending a $1000 bill.

The amount you spend is sent to the receiver's address.

The change is sent back to you on a new change address.

Change addresses come from a different list of addresses inside your Trezor than your normal receive addresses.

Your Trezor is operating correctly.