rubber/plastic interaction

Along with the Tandy 1000 that I brought home the other day, I also got the monitor plinth (just not the original monitor itself). Mounted on the underside of the plinth are rubber feet, and these appear to have "eaten" into the top of the 1000's plastic case. Has anyone seen this kind of interaction before? In the hundreds of vintage systems I've seen, I've come across many cases of rubber parts deteriorating (and sometimes turning to goo), but not of it damaging other materials (and in this instance the rubber feet themselves seem to be in good condition still) I'm not sure how widespread this is, and/or if it's going to be more of a problem as things age. On the other hand, I'm inclined to think that this is an isolated incident, and maybe related to aggressive cleaning materials used on the machine's case (which then softened the plastic) - there are more imprints on the case shell than there are feet on the plinth, so it happened at least twice with the plinth moved in the meantime. Thoughts? Jules