Generally the issue here is that somehow your page processes are creating model changes. This could be a new row made on page load, or some data change… Then in your model you have the “Prevent users from leaving page…” (advanced tab) property selected.
The trickiest situations occur with page includes. They don’t show up in your initial review of models, but once the included page gets called, all its models are in the page and will fire that unsaved changes warning…
Happy sleuthing.
