That's active and welcome but I can tell you already that unfortunately it's not the solution.
Why ?
Because you are modifying the core code of dokuwiki whereas it's a plugin issue.
How to solve it ?
Find what cause this behavior in the Farmer plugin and then may be correct it.
Third
As I said in my previous post, I don't have this error. The rewrite rule above gives you a clue, when you add a bang, the htaccess will add automatically a animal query parameter, if not, there is one added for sure.