There is a grand difference between seeing a rule written down and seeing it in practice: so while it might be a long-running house rule, this is arguably the first time it's really been an issue. (And when house rules of any sort lead to PC or favoured NPC death, things will always be different)
Furthermore, as has been said by others, since the nature of the spell was multi-turn non-dismissable damage he probably felt quite frustrated that for several turns he was "team-killing" and was unable to do anything about it - whereas the missed arrow for 3HP, annoying as it is, is not usually a life-or-death situation.
You've said your PC likes the tehory behind the rule but not the practicaility: speak to him more on this. Even if arguaging mid-game is bad form, he's clearly offering you some room to maneouver. The problem is that you and the rest of the group do have a certain amount of intertia in this house rule ("When I were a lad, we had to walk 15 miles in the snow to get a clear shot at the villains..." ;-) ) so he's going to have to work extra hard to come up with something to placate you - so try to cut him some slack! Even though he's in theminority, it's better to find something that makes everyone happy than something that makes him angry.
You're right, though, in that ultimately the exact rule doesn't matter - if pre-agreed, the players should not throw a strop in the middle of a session. I don't think this particular example is kickable, though, nad it's definatly something you should talk more to the guy about. (After the heat of combat is over, he might not be as tense about it anymore.)
Furthermore, as has been said by others, since the nature of the spell was multi-turn non-dismissable damage he probably felt quite frustrated that for several turns he was "team-killing" and was unable to do anything about it - whereas the missed arrow for 3HP, annoying as it is, is not usually a life-or-death situation.
You've said your PC likes the tehory behind the rule but not the practicaility: speak to him more on this. Even if arguaging mid-game is bad form, he's clearly offering you some room to maneouver. The problem is that you and the rest of the group do have a certain amount of intertia in this house rule ("When I were a lad, we had to walk 15 miles in the snow to get a clear shot at the villains..." ;-) ) so he's going to have to work extra hard to come up with something to placate you - so try to cut him some slack! Even though he's in theminority, it's better to find something that makes everyone happy than something that makes him angry.
You're right, though, in that ultimately the exact rule doesn't matter - if pre-agreed, the players should not throw a strop in the middle of a session. I don't think this particular example is kickable, though, nad it's definatly something you should talk more to the guy about. (After the heat of combat is over, he might not be as tense about it anymore.)