Our daughter spent the night at the home of her girfriend. Both are 14. The next day, they called and said the girlfriend's parents were taking them to the mall. Okay by us.
We found out later that the parents didn't take her to the mall, they took her to her 15-y/o boyfriend's house (she's not permitted to date), where his mother left the two of them alone for several hours. I'll let your imaginations wander as to what too place while they were alone.
All parents involved in this little subterfuge knew full well they were violating our boundaries, did it anyway, and lied about it when we found out. Needless to say the list of friends our daughter can spend the night with has been shortened considerably.
I'm sure their rationale for lying was "Well, they are too strict. They should let their daughter live a little". Translation: Our child is going to screw up and we are more comforted to see other children screwing up because it looks like it's not our fault.
My mother is all about this philosophy. She thinks all teens are like farm animals and we should just get used to it. No wonder we are all so screwed up.
Had one similar experience--son's teen girlfriend and her obsessed mother. Always wanted to maneuver more "private time" for the two young things. Had absolutely no support for my concerns about chaperonage--
I was barely able to control the situation--the only thing that saved the day was when the girl suddenly porked out after quitting the sports team. Teen boys dump fat girls.
Some family friends of ours when I was growing up had two daughters around my age. The parents had a firm rule: no "spending the night" at anybody else's house, ever. It was an excellent rule, since there's no good reason for a child ever to spend the night at another family's home (barring a serious emergency), and it eliminates the need for the parents to share with children their judgements or suspicions about the fitness of various friends' parents. It also eliminated the "but, WHYYYYYYYYYY?" routines when the answer was no. Invitations never even got referred to their parents; if someone said "maybe you can spend the night at our house", the girls just said "we're not allowed to spend the night" and that was that. At the time, I thought it was unnecessarily strict; now I'm quite sure I'll apply the rule to my own children.