Never a corner. The foul was given for Wanyama pulling a defender's arm I think.
The non-corner we are agreed on. I've watched the replay of that goal several times and I'm blowed if you can call the piddling amount of pushing and shoving from either team during that corner as worthy of blowing up for a foul. My contention is, is that Mike Dean has not allowed Saints to profit from his error.
On the pure subject of disallowed goals from corners, we've had this a few times before. Last season, Maya Yoshida scored from a corner and was deemed to have pushed the goalkeeper when it was the goalkeeper who pushed him. And the pushing amounted to nothing, in any case. And in another game, Jason Puncheon scored a header from a corner, and occasionally I go back to see if anything has magically appeared in the video that convinces me that it was anything bar a goal, because nothing happened.