debian-builder behavior is normal: php5-imap is in feisty universe, and didn't get any security issue fixed in feisty-security. So it doesn't exist in "feisty-security universe", and can't be found in feisty (because you only added "main" and "restricted"), therefore debian-builder used your dapper deb-src line.
This is not a bug then, closing the report.
> /etc/apt/ sources. list : gb.archive. ubuntu. com/ubuntu feisty main restricted security. ubuntu. com/ubuntu feisty-security universe
>
> deb-src http://
> deb-src http://
debian-builder behavior is normal: php5-imap is in feisty universe, and didn't get any security issue fixed in feisty-security. So it doesn't exist in "feisty-security universe", and can't be found in feisty (because you only added "main" and "restricted"), therefore debian-builder used your dapper deb-src line.
This is not a bug then, closing the report.