It's not really stealing of source if you wrote it and there's no contract saying it belongs to them.
I know in Canada at least, unless otherwise stated copyright stays with the creator (in a contractor relationship, other way around for employees) and you've simply licensed them use of the code. So you're only bound to anything you've verbalized (that can be proven) and written down (think emails). I know our copyright laws are a bit different from the US though, so it's worth being prudent first (always is :).
I know in Canada at least, unless otherwise stated copyright stays with the creator (in a contractor relationship, other way around for employees) and you've simply licensed them use of the code. So you're only bound to anything you've verbalized (that can be proven) and written down (think emails). I know our copyright laws are a bit different from the US though, so it's worth being prudent first (always is :).