It was the combination of Bamber's deal with Liverpool (Bamber wanted to go down as the first Brighton chairman to be involved in a £1 million transfer deal), the fact he wanted to make several of Mullery's coaching and backroom staff redundant and the inference that he wanted more of a say in...
No, Ron Atkinson had already taken over from Dave Sexton at Old Trafford. It was with Big Ron that Mullery had done a deal with when Bamber went behind his back.
He's our Alan Mullery* of this decade. Once he goes, it will never be quite the same again for him or us, even if he came back.
* although Mullery didn't pimp himself for available jobs the way Poyet appears to have.