Judging from all the comments, this is situational. I have a pair of MX4000s that I use when I want noise canceling, and aside from being finicky and slow to reconnect sometimes, once they're connected they're fine. No random disconnects.

But I can also walk halfway across my house and bluetooth doesn't drop until just about the time I reach my refrigerator, so I may have an exceptionally low noise floor where I live.