Freelance / Contractor - Who "owns" the source code (fla)?

I’m sorry if this is the wrong forum, but I did not see a “general” forum.

I’m new to freelancing (Flash/AS). When you develop a site or app for a client, who “owns” the source (fla) files?

I did a site for a client a few months ago. It reads a SQL database and loads images, text, and links. It also builds the containser, dynamically, so the user can create as many as he wants. I think it’s pretty slick & dynamic, and I would like to retain control of it. Is this an accepted practice? What is the “norm”?

For this instance in particular, my partner was a contractor who sub-contracted out to me. His consulting firm had a contract with the client. The ownership of the source files never came up.

Today (several months after turnover), I got an email from another developer from the client. He said he needs to do some “tweaks” to the site, and asked if I would mind giving him the source files.

Suggestions / advice?