This question already has an answer here:
I am deploying a contract from a Parity instance that has several accounts within it. When I deploy a contract at the console of the same computer, Parity UI asks me for a password to unlock the account.
And then sometimes when I add a new account, it asks for this password instead.
How does Parity choose which account to debit to deploy from (or is this an ETH thing and not Parity specific)?