During the set up of my blueprint I stumbled upon the feature to reorganize the construction code execution line. Just for fun I created two of these blank nodes and connected the first node with the second node. I expected that nothing would happen, but the entire engine froze. It does not do any work, it just stopped executing anything as if the engine had entered a deadlock. I assume that this is a bug. I did not know how to search for this bug, so I do not know whether this was already reported.
Since I can not accurately describe the situation, here is a picture:
Oh yeah, I have reproduced it by doing the same steps as mentioned above.
I could not do anything - not to speak of saving my files - and had to kill the engine process through the task manager. While this may be rare, doing what I did can still happen by accident.