Wis. Stat. § 7.24: Title to election materials.

The filing of a nomination paper, ballot application, financial report, affidavit, or other form or statement with the appropriate official or agency responsible for accepting such materials under chs. 5 to 12 irrevocably transfers the legal title to such official or agency, regardless of the sufficiency of the filing. The official or agency shall retain all election materials until destruction or other disposition is authorized under s. 7.23.