[Sombre]

My current thinking is that I've probably misunderstood what researchlevel -1 actually means. I thought it meant the spell would not appear in research and not be castable. But I suspect it actually just means it's like a holy spell - doesn't appear at level 0, but you still already know it and can cast it.

If this is the case, the 'eagle eyes' you were casting was actually a copy which was designed to work as a onebattlespell and never be castable. So eagle eyes (if researched) should be showing up in your castable list twice.