Dang! That would definitely give me reason to be concerned. I haven't seen anything at all happening like that on the Roadrunner. Maybe you were right about some kind of 'chemical' reaction with those signs you used. I don't think it's an issue with the stuff we used. The car spent 2 years sitting outside in heat, rain, snow, etc... I never did get around to putting any on our other vehicles but have always meant to. - Even stored inside it might help keep mice out. I guess I'll have to be watchful to make sure nothing weird goes on.