Hi Raldo
My process is perhaps a bit simpler than yours (and Marko's) and different from most, in that I don't directly tag anything into [Keywords] in either program - I don't actually use keywords, just the dedicated fields for Artist, Album, Places, People etc. So while I have not seen what you report, my workflow is different so doesn't mean it's not reproducible.
I simplified my photo tagging to just Date/Album tagging (directly in MC, as well as a few me-specific fields) and People (facetagging, in lightroom). So when tags autoupdate in MC after tagging people with lightroom, people names go into both [People] and [Keywords]. I have been meaning to try the geotagging plugin you've mentioned too - which tag/s does it store info in?
It does sound to me like one of the lightroom steps might be culprit - what happens if you do the geo-plugin earlier in the process and then add faces, keywords etc? Do they still end up scrambled? I have not seen Lightroom by itself strip slashes or delimiters, but I am definitely a relative novice with the program! Could have a look at Preferences > File Handling > Treat '/' as a keyword separator?