Board Thread:The Quarters - Q & A/@comment-67.173.253.197-20160317185342/@comment-24150802-20160320010844

The To-Dos reappearing as undone would have been because of a sync error or (more likely) this local storage issue. The browser would have been unable to sync to Habitica's server, which meant that any actions taken in the browser were displayed but then later were reverted when syncing started happening again.

This isn't specific to challenges; it could have happened to any tasks.