Error moving a Task from Inbox to a Project.

Add a task to the Inbox. Go to Inbox, and double-click on the new task's Project field. Select the first Project in the drop-down list (in my case, Single Tasks). Click OK. Task remains assigned to Inbox. Selecting any other Project besides the first works just fine. My workaround has been to create a dummy "---" project as the first in the list, but I'd rather it worked correctly!
Thanks,
Carl