It’s not necessarily about the environment being toxic. I’ve had the same experience with co-authors. It’s just human nature to forget things other people tell you, and then to suddenly have the idea yourself....
To me the problem was the "I won't do it if it isn't my idea (and so other people have to go out of their way to trick me into thinking their idea is my idea so I don't discard it)" aspect (which I find extremely toxic), not some kind of "I (maybe even accidentally) took credit for your idea because (but if you had corrected me I'm sure it wouldn't have been a problem)" angle.