This is hard to reproduce, but I think the "Suggest Bits of Code" (BOC) feature is fighting the "AutoComplete" (AC) feature. Let's say I've typed in this much:
ITreeLevel* pTreeLevel = LookupTreeLevel(pNMTV->itemNew.hItem);
ASSERT_POINTER(pTreeLevel,
Now, BOC suggests "ITreeLevel" - excellent! But, if I type an "I" by accident (instead of hitting <Return>), BOC disappears, and "AC" suggests "INT"! Oops. I would have expected BOC to stick around as long as the letters I've typed match its suggestion.