The time delay and popup is only after a key letter, like '.' or '"'.  Having the box appear whenever one pauses would be maddening.  I have the delay set to .1 second.

The list is not supposed to shrink. Having everything disappear on a typo would not seem good to me.  But it might be possible to visually separate remaining possibilities, so when only one option (or none) is left, it is visually obvious.  Once the overt bugs are fixed, it would not hurt to review details of intended behavior, perhaps with some review of other completers.