I have read on a couple of different forums that Tamron have a 'fix for AF issues'. Apparently you need to send the Lens to Tamron and there is a 3 day turnaround - user pays the postage to Tamron and Tamron pay the postage back to you. Here is a quote I saw on one forum:
"This firmware update is intended for all those buyers of this lens that had them shipped before the February 8th recall of the Canon mount lens. Any lenses that shipped after April 20th should already have the update installed. All Nikon mounts also have the firmware update already so you can save yourself the shipping costs."
Not sure about lenses shipped between these dates
but it could mean they may or may not have already been done.
Here is another quote
"called Tamron and was told that the lens fix was a re-chip and it fixed various other problems. He was told that weather or not he was experiencing a problem it should be done"
Note everything I have seen on this 'fix' is on the other side of the pond - not seen anything from user in Europe about it.