iMovie '11 - Move Events From One Hard To Another, Loses Keywords!

Hi. I've been importing lots of video on to my iMac's hard drive, keywording the Events, and then moving the Events to an external hard drive using iMovie's Event Library.

My problem is, once I've moved the Events, all of the keywording I did on them is lost. Is this what's supposed to happen? Am I doing something wrong?