LisUkn when merging 2 pwads

[SilverMiner]

If I get it correctly, -join is meant to merge 2 pwads.
So and I do that like "deutex -join a.wad b.wad"
And it stops on LisUkn word.

1. Is this an intended behavior or something is wrong?
2. How do I merge 2 pwads if I do something wrong?
   Here's a pic from cmd