The ruby solution returns "Left side wins!" when I am checking it. I tested the exact solution that is used in random tests. There are 38 people who finished it successfully. Maybe there is some bug in your solution.

Thank you for solving. Please could you grade this kate if you havent already :-)

I tried a few solutions in Ruby, all these solutions give: Passed: 208 Failed: 0.

Your code is not indented so it is not easy to follow.
AFAIK you have this line in decode str = help(t) and in function "help" t << ("\v" * ((n*n)-l)) so you are introducing yourself lots of \v in the input string you have to decode, hence you modify the input string with \v.... Moreover the \v have to be added when you code not when you decode. Hope that help.

There are never "...\v\v\v\v\v\v\v\v\v\v\v..." in the decoded strings. The test are the same in all languages.
Do you modify the input string in place?

Nobody can't accept an issue without an example of the failed tests, sorry for that. The tests are the same in all languages and 263 guys passed the kata.