Hello ,
I could not reproduce this issue on our end. However, I tested this in the 4.8.2 version of the engine. I have also included my setup below. If you are using 4.8.2 and it is a project that has been upgraded from an older version of the engine you can try using the “Refresh all Nodes” feature. This can be found by opening your blueprint and going to file > Refresh all nodes. I hope that this information helps.
My test setup:
I used a gate that opens and runs a loop with a .01 delay when I press the middle mouse button. This loop will continue to print out the mouse position until I release the button. I tried holding the middle mouse button and then left and/or right clicking, however the release execution only fired off when I actually released the middle mouse button.
Make it a great day
Edit: Fixed attachment