When you upgrade a unit....

What happens exactly?

lets say i have a Moon well. this unit is in the trigger group "Wells"

when i click the "upgrade to Improved Moon well" button,

while it is upgrading, is it considered Moon Well or Improved Moon Well?
will the new upgraded unit remain in the "Wells" Group?
will it keep custom value?

Well, I'm almost positive that it's considered a regular Moon Well. I don't think he remains in a 'Wells' group, if that's a custom group. Custom value? No idea.