Sorry, i did not test it this extensively.
I noticed that after i mark my items, bug occures, tried a couple more times, it reproduced.
Then i went on reinstalling spree, starting with backups (because i did not want to loose all my marks). I "reinstalled" mod and saved variables (in different combinations).
It kinda did the job (no bug so far). So i think it was something local that "broke" addon.
Just in case, heres a saved variable for "damaged" version (i believe it is, its from minion backup)
FCOItemSaver.lua