When I open a grid with a parent collapsed/closed, and drag an item to become it's sub-item, just the new sub-item shows (not any other children).
This is often *very* helpful behaviour, but has been initially confusing to me, and others - when you dont click what's going on.

 

Example:

the two blue item were dragged under "241 Final" which has many other sub-items
 

 

Suggestion:

In the above scenario, two sub-items show, but others are hidden -
[1] instead of showing the dot (indicating expanded) beside the parent item, continue showing the > arrow which indicates item collapsed. This would be a clue for those who are bewildered by this behaviour. Clicking on the arrow would then show all sub-items.

Another related situation [BUG]:
I initially dragged an item to become sub-item of "241 Print" (yellow in the example above). I realise it's the wrong parent and move it to the correct item. "241 Print" still shows the dot indicating expanded (but showing none of it's sub-items), instead of the arrow which it should show.

 

can add to mantis if you want...