To reproduce:

auto revisioning must be enabled or you must create a new revision when editing this test node.

- create a node
- un-select 'automatic alias' and submit
- edit the node (note that automatic alias is still disabled) and submit (I did this twice but I imagine once is good enough)
- revert to the first revision

BUG = This reverted node will have automatic alias enabled and a populated alias field even though none of the original revisions had aliasing enabled.