This bug has been reported on Ubuntu Launchpad as: https://launchpad.net/bugs/443296 from the launchpad report: Selecting multiple archives and selecting extract here (in thunar) only extracts the first archive, if using Xarchiver as default archive manager for this action. 'xarchiver' version 1:0.5.2+20090319+dfsg-4 Xubuntu 10.04
Xarchiver provides the tap file with those settings, and I guess xarchiver is dead anyway.