This problematic Polish special characters are: "ł" "ż"
I the old version editor I write them using combination of keybord keys :
"Alt" and "l" = "ł"
"Alt" and "z" = "ż"
Unfortunately, this combination does't work in the editor xenforo 1.2.0 RC1 (i have to copy and paste them from another program to put them here).
If think that now this two combinations have some special functions in the editor and that's why there is a conflict.