It has to do with the fact that the flags have to be maintained (specifically, the +e flag) -- if your branch was expanded, and you replaced it with a line that was not expanded (didn't have the +e flag) then this thing happens. It's sort of a bug, (the control should actually have been redrawn) but it's also something you can fix (by making sure to preserve the +e flag if it's there)
Future versions will have the ability to set the properties of an item individually.
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