Feel that people are blowing this out of proportions - This was going on for 10 minutes today, everyone got the popup to join a mission for those 10 minutes or so. A few people might have had their original mission abandoned and able to start it over, but I haven't heard of anyone still doing their new mission or even being able to.
With that being said - I clicked redulite again to close the window - I still had my original mission open just for the fun of it to see how many points I would get to and nothing happened so I continued killing mobs and went about my day, think more people should do the same