Does anyone know why the "tripod detection system" would stop working?

As you can see from my other posts, I went to shot Garwin Falls yesterday. I forgot to turn off my IS on the 5DIII + 24-105 combination. I usually do turn off my IS while shooting from a tripod, but I occasionally forget and I've never had a problem.

Until yesterday. About 90% of the shots from a tripod have incredible amounts of blur in them. I wish I would have taken the time to review my shots in the field, but I didn't. After seeing this last night, I thought it could be my tripod slipping on the ice or the IS issue, so I did several test shots around the house. About half the time, with IS on while mounted to a tripod, I had significant blur whereas with IS off, the pictures had no blur each time. I've been through the 5DIII manual and it indicates that there shouldn't be a problem because of the "tripod detection system," which was my understanding

I've tested my 70-200 f/2.8 II, and did not see the same issue. So, it could just be the 24-105 lens.

And, for the back story, I did slip on ice with the 24-105 about 3 weeks ago trying to get a shot for the "Near/Far" assignment. It seemed that the hood protected the lens, but I am wondering if perhaps this is the first sign that something internal is out of alignment.

Any thoughts?