Canon UK has put the Canon EOS camera and lens compatibility issue into English for us:
FAQ: Peripheral AF points operation limitation with certain EF lenses Issue
When using any of eight zoom lenses listed below released between 1990 and 1995 with any of the listed cameras, the peripheral AF points do not function as cross-type AF points resulting in vertical and horizontal lines not being simultaneously detected. Vertical or horizontal lines can only be detected separately.
Affected products:
Cameras
EOS 7D EF 35-80mm f/4-5.6
EOS 40D EF 35-80mm f/4-5.6 II
EOS 50D EF 35-80mm f/4-5.6 III
EOS 60D EF 35-80mm f/4-5.6 USM
Lenses
EF 35-80mm f/4-5.6
EF 35-80mm f/4-5.6 II
EF 35-80mm f/4-5.6 III
EF 35-80mm f/4-5.6 USM
EF 35-105mm f/4-5.6
EF 35-105mm f/4-5.6 USM
EF 80-200mm f/4.5-5.6 II
EF 80-200mm f/4.5-5.6 USM
Cause
This is due to the optical characteristics of the camera’s AF sensor and lens. If the maximum aperture of the EF lenses and EF-S lenses other than the lenses above is up to f5.6, all of the AF points function as cross-type AF points, and both vertical and horizontal lines are simultaneously detected.
Answer:
We would like to apologize for not including this information in the user’s manuals of the affected cameras.
I think that you will also find the following Tamron lenses to have the same issue:
Tamron 17-50mm f/2.8 VC Lens
Tamron 60mm f/2 Macro Lens
Tamron 70-200mm f/2.8 Lens
Tamron 10-24mm f/3.5-4.5 Lens