It seems that when inflicted damage is low the eventhandler is executed twice...
If you shoot a guy on the legs with M16, it causes a damage of about 0.11xxxx and the EH is executed twice...
But when using some more powerful weapon, which in this case was some knife addon hasle (throwable knives) that caused a damage of 0.66xxxxx when hit on the legs, the EH got executed only once...
And if the soldier dies from the hit the hit EH is executed only once...
Not the most extensive research data
But would seems that there's a slight bug in hit EH...