rar archive - add or remove files bug?

[scud]

I have problem with adding files or removing files from existing rar archive. I set in packer options external rar program to be WinRAR, but when I open some rar archive (example left panel) and (from right panel) try to copy some files in that rar archieve I got message "Function not supported!" I do the same thing with standard Total Commander and all works fine with rar (adding and removing files from archive). Please help.