This is probably related to an earlier post by Pieter.
When I do a dot-lookup for column names for a table, sometimes it gets into a mode where you start typing in a letter and the list disappears (as if nothing matched). Then I do it again, type in the exact same letter, and it works.
And other times in the list I will arrow down to the name I want, press enter, and nothing gets entered.
Then another time just pressing the arrow key will make the list disappear.
This is something that has changed in this 6.0beta that used to work.