This appears to be close to a repeat of FL-2458 - every time http://bazaar.launchpad.net/~compiz-team/compiz/0.9.12/tarball/3958 is downloaded it has a different resulting filesize (also bazaar.launchpad.net never responds with a length for the file), causing a verification failure.

I reached out to the compiz-team launchpad group and got a couple responses back indicating that the 'download tarball' URL is rebuilding the source tarball on the fly each time it's downloaded, including directory and filesystem metadata creation, so it's going to have a different size. Both people responding suggested using the non-bazaar-backend URL https://launchpad.net/compiz/0.9.12/0.9.12.0/+download/compiz-0.9.12.0.tar.bz2 instead (which is from https://launchpad.net/compiz/ -> select version -> select file from list of source releases under 'Download files for this release'), which is both reporting a length and consistently providing the same tarball, at least for me.

Build log for a verification failure during attempted merge attached.