Which version of OmniFocus do you have installed? This sounds like something we fixed for the 1.0.1 release, which is available here:
http://www.omnigroup.com/download/latest/OmniFocus.dmg
If you have that version installed and are still seeing this, can you send email to
omnifocus@omnigroup.com? We'll be happy to work with you to figure out what's going on here.