This story is nothing new in Wisconsin. The police arrest people for just about anything on their person if the officer wants to say it was a "concealed weapon". This is why a year or so ago a judge in Wisconsin ruled that the concealed weapon violation law was unconstitutional. It is overly broad and allows just about anything to be construed as a weapon. There is a case in Wisconsin of a 10 y.o. being arrested for having a lock in one pocket of her coat and a shoe string in the other with the coat locked inside her school locker. It was overturned at the appeals court but the whole thing is ludicrous.
I know one person who has two concealed carry convictions for a pocket knife and they weren't even in his pockets. One IIRC was in the console of his car and the other in a tool box IIRC in the trunk of his car.
Keep in mind there are only three elements to this violation:
1) It is hidden from normal view
2) You know it is there
3) It is within your reach
So...as soon as you put your gun or bow or knife in a case you just broke the law. As soon as you put your gun in a gun safe and are within reach of it you just broke the law. The law is unconstitutional and should be repealed.
To answer your question about fighting it...Absolutely! Don't let it go. Remember that politicians often create laws to make previous convictions have dire consequences in the future. If you plead guilty or no contest to this and a year or more down the road they make all misdemeanor convictions for concealed weapons a "Gun Free Zone" you will be barred for life from ever owning or touching a firearm.
Remember: 1) Never talk to police...EVER
2) Record EVERY interaction with the police on a video/audio recorder. Preferably have a DROID or something that transmits the video/audio as it is happening so they cannot take your evidence and destroy it.
3) Know your rights. All of them.
Good luck to you!