How to stop completion menu from disappearing on a colon (:) ?

[a-torgovitsky]

The title pretty much says it: If I type abc: , completion comes up at a, but then disappears at :. How can I change that behavior so that the menu doesn't disappear at :? I thought that maybe this has to do with trigger characters and tried the solution in this thread but that didn't do it. Is this a different concept than a trigger?