PPA Question - Distribution Field

[Will Daniels <mail@xxxxxxxxxxxxxxxxx>]

Hi, I have built a source package for which I want to build binary packages for both gutsy and hardy.  The Debian Policy Manual suggests that I should be able to use a space-separated list of distribution names in the changelog (and thus .changes file) to specify this.  However, the package was rejected by launchpad saying:

"Unable to find distroseries: hardy gutsy"

Before this, I had tried just rebuilding the same package with the same version for gutsy, but launchpad didn't like that either (I had originally build and uploaded the package for hardy only):

"MD5 sum of uploaded file does not match existing file in archive"

It doesn't seem right to change the package version just to use it for another distribution, and I'm not sure whether launchpad would keep my original hardy package in that case either.  So, what is the correct way to do this?  Do people normally change the package version when backporting?  Is it just a limitation of the PPA system?

Thanks for any help in advance,
Will