[Kameron8]

I believe it overwrites effect tiles if they have a higher level, which is probably what's happening here.

Should it change? Maybe? There might be similar interactions between cinder tiles/etc.

It should either always overwrite or never overwrite -- trying to establish tile dominance with a skill's level which may or may not equate to the ice tile's level makes life harder on everyone. Unless ice skills from swordsmen are inherently supposed to be more powerful than ice spells cast by mages, I'd heavily support changing it.