Duplicate, but verified fixed in //UE4/Release-4.11/2826901
If you have a Blueprint with a pre-existing component, then add that to a map, and copy it, OnHit events in the COPY will also trigger in the ORIGINAL.
According to the licensee, this happens with ACharacter, which has exisitng components or AActor with a component added in C++, I only repro'd and confirmed the ACharacter case (Repro steps and more explanation included)
1. Create Blueprint from Character class
2. Add OnHitComponent for the Capsule and wire up a Print String to display the Self variable
3. Drop one of these in a map. Name it "ObjA"
4. Alt-drag to copy it. Name it "ObjB"
5. Run the player into each placed Blueprint
Hitting ObjA prints "ObjA"
Hitting ObjB prints "ObjB" AND "ObjA"
*If you set the Debug filter to ObjA and add a Breakpoint for the OnHit event, it'll trigger the break even when bumping into ObjB
*If you drag in a fresh Blueprint "ObjC" rather than copy, this problem doesn't occur.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-24932 in the post.