This reminds me of a reddit post from about 10 years ago where people started to notice that when they get decaf coffee at work it sometimes bleeds through the styrofoam cup while the regular coffee never does. There have been several other reports of this since. The most credible theory was that sometimes there is solvent left over after the decaf process:
https://www.reddit.com/r/mildlyinteresting/comments/2m2fiy/o...