A Wisconsin judge's decision to become Facebook friends with a woman whose child custody case he was hearing created at least the appearance of bias, a state appeals court ruled Wednesday in ordering the case to be re-heard by another judge.

The case, which is the first of its kind in the state, contemplates whether judges' use of social media can compromise them. In its ruling, the 3rd District Court of Appeals didn't lay out any bright-line rules for judges, but it warned them to use caution when engaging with people online to avoid the appearance of impropriety.

"We caution that judges should recognize that online interactions, like real-world interactions, must be treated with a degree of care," appellate Judge Mark Seidl wrote in the ruling.

According to court documents, Angela Carroll filed a motion in Barron County in 2016 to adjust a custody arrangement she had reached with her son's father, Timothy Miller. She demanded sole legal custody, primary placement of the boy and an order forcing Miller to pay child support. She argued Miller had abused her, an accusation Miller denied.

The case landed with Judge Michael Bitney. Three days after Carroll and Miller submitted their final written arguments in 2017, Bitney accepted a Facebook friend request from Carroll.

She proceeded to like 18 of the judge's posts and commented on two of them. None of the posts were directly related to the pending custody case. Bitney didn't like or comment on any of Carroll's posts and didn't reply to her comments. He didn't deny reading them, however.

Carroll also shared one third-party photograph related to domestic violence. Nothing suggests the judge ever saw it, but the post could have appeared on his newsfeed, according to the documents.