I had two rooms, and decided to move npc_rat_1 from one room to another. I tried dragging the object in the room/object tree list from one room to another, looked for a move/up down set of buttons, nothing.
So then tried cutting and pasting. I clicked the object name (npc_rat_1) from one room, selected Cut, clicked the name of the other room, selected Paste, and the name changed from:

npc_rat_1

to:

npc_rat_

Thanks for reporting this. It's to do with the automatic renaming feature - if you copy an object multiple times, it will add a number onto the end. So if your object name already ends with a "1", this will be chopped off and then when it's pasted it may end up with a different number if there are already other copies. If there are no other copies, it won't add the number back again.

If you cut and paste an object with a name that doesn't end in a number, it will have its full name when pasted.