Hi! This mismatch happens in current unstable as well, breaking any multiarch that involves this package.
Turns out this is caused by missing either Build-Depends or Build-Conflicts on docbook-xsl. You did a source+amd64 upload, and apparently your home machine had docbook-xsl installed, while buildds do not. Ie, we need to either have docbook-xsl installed on every build (Build-Depends) or on none (Build-Conflicts). -- An imaginary friend squared is a real enemy.
