To remove a package it needs to be found in the top list, the search entry helps here but even better would be if when the user clicked (or possibly double-clicked) an entry in the image contents list the matching entry in the packages list was shown.
Fixed in http://git.yoctoproject.org/cgit/cgit.cgi/poky-contrib/commit/?h=shane/hob2-v0.10&id=8523721719ba80dbf1d700b4003714130fa7be61
It was in the master.