FYI, colophonium is called “rosin” in contemporary English, at least in the contexts of electronics, music, cooking, and sports. (In English, colophonium is considered an archaic word for it. Most people won’t know it. I only do because of German.)
Rosin doesn’t evaporate. (Give it enough time and it becomes amber, remember?) So it is necessarily the solvents that are escaping. I guess a better bottle wouldn’t hurt. Glass would work, but my flux came in HDPE bottles, and it’s fine several years later. Same with IPA stored in that.