Strange Canon 50mm f1.4 problem

I took my 50mm for an outing yesterday for the first time in a while and was gutted to discover that it has suddenly developed a focussing problem.

Photos taken close to the camera (5DII) are sharp but anything more than 3m is way off. I never had the problem with it before and don't think that it can have racked up more than 200 shots in its life so am a bit surprised. It is always kept in the bag, has never been dropped or abused and looks as good as new. I have tried my 24-105 and 70-200 and neither has a problem on the same body so I am 99% certain that it is the lens.

Is this a known issue with the lens? Has anybody else had something similar? I did a search and found numerous reports of broken USM motors, but this seems to be working fine. It will lock on focus for each shot, but just seems to be off.

Adjusting the calibration doesn't seem to be a good idea as it seems to be good for close subjects.

It is out of its warranty period but I know a guy who may be able to assist. I was just curious if this was a known problem with the lenses before I ask him for a favour.

Thanks for any input.

How sharp is it for distant subjects using MF?

Its hard to get locked on perfectly. Will try tonight with live view and a tripod.

This is actually a quite common problem with the 50mm 1.4. I know a friend who also had a similar problem and he sent it to Canon even after warranty, and they gladly fixed it for him.