Canon 135mm f/2.0 Back-focus issue

[taschrief]

I currently own two digital bodies (T1i, XSi) and an Elan 7NE film body. I have been shooting a lot of Canon primes lately and have come across an issue that puzzles me. I just picked up a Canon 135mm f/2.0L and it back-focuses a bit, ON ONE BODY!. From f/2 to 4.0 or so, the depth of field is so narrow at distances less than 25 feet, that the picture is ruined. At f/5.6 and narrower this is not an issue. The really puzzling thing is that it happens only on my XSi; the lens functions perfectly on the T1i. In order to eliminate variables I shot the same camera settings on each body with several lenses. I also compared my (all Canon) other lenses: 200mm f/2.8L, 100mm f/2.8 Macro, 85mm f/1.8 and 50mm f/1.8. All of theses lenses work just fine on both digital bodies. I haven't had a chance (or the money) to do all of this over again with film. This is the only lens/body combo (135/XSi) that I have this problem with. I own several zooms (70-300, 10-22, 28-105, 18-135) and this issue has never come up before. Granted, none of those zooms opens up the the f/2 - f/2.8 range.

Is there anything I can do with a lens that back-focuses on one body and not the other? If I send the lens/XSi to Canon for adjustment, would that mean it would no longer work properly with all my other lenses? Any help/suggestions are greatly appreciated.
Thank you.

[OsmosisStudios]

Theres no real way to correct that on those bodies other than sending both bodies and the lens to Canon to have them calibrated. Higher-tiered cameras do have a focus correction system built in.

The problem is very simple, and explained rather well by the guys at LensRentals