I spent a large part of last weekend stripping wallpaper and removing
crown molding and chair rail from my dining room. I was surprised to
find that the top of the drywall is about an inch and a half short of
meeting the ceiling in that room. From a redecorating perspective,
it's not that big a deal since we'll be installing pressed tin
ceilings with a cornice, so the gap will be covered again, but I've
never seen this before.

The ceiling gives a little when I push up on the edges, but seems
sturdy in the middle; the whole ceiling doesn't push up.

Is this common? Is it a sign of poor construction? Is it something I
should rectify? Does anyone know if there's any kind of insulation
value lost from having it this way?

TIA for any opinions/information!

--
Jennifer