source taken from UO Kingdom

Casting Field Spells such as Poison Field and Fire Field dont always land where there supposed too if the ground is targeted. In malas outside luna near the eastern entrance you target the ground and the field ends up a screen to the west. This isnt the only place ive seen, Malas snowy region also does this in some spots.

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there are even some areas where you can't cast field spells at all. In Tokuno at the Hiryus and Lesser Hiryus there is nearly no chance to succesful place a field spell or an EV somewhere. Sometimes it works when I target a plant or some special grasses.
The same happens in some dungeons, e.g. in Shame I can't cast a single EV nor a field spell.

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There are a lot of places you cant cast fields or EVs. Someone on another thread I was reading last nite said if that happens cast it on yourself and it works every time. Have not been on UO since to check it out....but you might give it a try.

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We just squashed a bug that was preventing you from targeting the ground in some locations - you'll see it live in the next patch or so, and it should make field spells (and EV, BS, and mining, etc) work properly.

E. Jeremy Dalberg
UO Community Coordinator
EA Mythic

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Yay, the first bug that I've reported that I've seen get fixed soon after me reporting it (did it through the beta client). Yay!