The chameleon tongue can and will stick to anything. It really just depends on how they hit it as to whether or not it is going to stick. In extreme situations tongue injury, even amputations from tongue mishits. These are fairly uncommon though.
On the other hand the chameleon tongue can be quite strong. I have had my female veiled attack my face. I guess after a year plus she realized I was feeding her and I might possibly be a food item (?). I was cleaning out the bottom of her cage. She approached me, I already knew something was weird with that. As I looked at her I saw both of her eyes where locked on me and the tongue was on the tip of her lips. Before I knew it she hit me with her tongue and some how managed to pull her entire body onto my face. I have witness something like this before on T.V. as well. A rather small chameleon was going after a big grasshopper. He hit with his tongue, the grasshopper did not give and he pulled himself onto the grasshopper who was on another branch.
I personally would recommend that you just moniter your chameleon over the next month or so when feeding. You may have just witnessed a rare occassion or there could actually be something with the ropes themselves. I personally think you may have just witnessed a rare occassion.
On the same subject I don't like ropes to much. I noticed that my veileds claws would sometimes get stuck in them and just dropped the whole idea of using them. I do on the other hand know quite a few people who use them and have no problems.