https://en.bitcoin.it/wiki/Change
Say that 1 BTC was sent to your address A and you send 0.1 BTC to address B.
The whole 1 BTC has to be taken from address A ( that's how bitcoin works ).
So Armory sends in the same transaction the 0.1 to B and (0.9 - fee) to a new change address C it creates for this purpose .
Say that 1 BTC was sent to your address A and you send 0.1 BTC to address B.
The whole 1 BTC has to be taken from address A ( that's how bitcoin works ).
So Armory sends in the same transaction the 0.1 to B and (0.9 - fee) to a new change address C it creates for this purpose .
In this case there is a TxIn that redeems your 1BTC UTXO. A 0.9 UTXO is created on the change address. The net effect on your balance is -0.1 BTC, but the change address is oblivious to the spent amount, it only knows its new 0.9 UTXO.
Look at the funding transaction you say is different in amount. Double click on it and look at the change address and its funding, then compare that to your wallet address ledger.
