Here are specific steps for recreating the problem in ubbthreads 7.1:
1)Start with default English language. Search island should be enabled in left or right column.
2)With language editor go to generic.php file and change encoding to 'windows-1251'
3)With language editor go to file portal_islands.php, find ADVANCED_BUTTON key, and change string 'Advanced' to any other string containing Russian letters, for example to Сложный. Without Russian keyboard layout one can use copy and paste to enter new string.
4)Try to use Advanced button in search island. For me it started malfunctioning after steps 1,2, and 3.
Step 2 may be omitted with the same result.
