This happened a few years ago, but I was recently reminded of it.
DH's sister was hosting Thanksgiving. We live out of town and at the time we were having car issues, so we told SIL about 3 weeks before Thanksgiving that we weren't sure and we'd let her know closer to the date. She mentioned that she'd be travelling for work during that time, so we could just pass the information on via MIL (who we called every day and who SIL spoke to regularly).
About a week before Thanksgiving, we discovered we could borrow my mother's car so we told MIL we were coming. When we arrived for the weekend, we saw SIL on the Saturday (day before Thanksgiving dinner) and she was a little pale. Turns out MIL had told her we would NOT be coming so SIL had issued an invitation to DH's cousin and his family, so Thanksgiving was going to be cozy
MIL did it on purpose, because she wanted her nephew invited (he and his family had newly immigrated and I think she thought it was bad manners to exclude them), so she manipulated SIL, but DH and I were left feeling awfully.
MIL is obviously in the wrong, but looking back I think we were too. We should have told SIL we were coming directly instead of trusting MIL, even though SIL was fine with that type of communication. I know my MIL and she is not opposed to manipulating people as she sees fits (she also once declined a wedding invite for us before my DH ever saw it).