How are multiple switches in "or" setup functional?
Your switches are in parallel as the other answer.
You only have 1 phase of power - so there is no way the same phase can be out
of phase with itself in your example.
I would venture a good guess a DIY'er replaced the 4 way switch with something other than a 4 way switch like a 3 way or something else and passing through the hot to the load. 
While not a code violation - the possibility that something could pose an issue exists .. my reasoning is that it is not normal and I suspect a DIY'er was in the switch boxes and wired things - the possibility to have a live wire floating around or some other unknown is enough to make me fix it right.
So here is what you should do to fix that - take a look at the wiring of the switches and see if they match the drawing below. 


Grey in drawing is Neutral (really your White wire), Red is your travelers (they are hot at times), black is the hot wire, green or copper is ground.

Example 4 Way Wiring source first load last: