Hypothetically, chas vshalom, if somebody eats milk and meat together, let’s say hamburger and Parmesan or some other “sharp” dairy that means you have to wait between milk and meat, are they milchig or fleishig or both? What can they eat after?
The person is now both milchig and fleishig! So if this was accidentally done, the person will now be vegetarian for the next six hours! By the same means is someone ate fleishig at 12 pm and mistakenly ate parmesan cheese at 3 pm, the person will be fleishig until 6pm and milchig until 9pm. The rationale for this is because we wait 6 hours after eating meat and hard cheese because they both leave a taste in the palate and through for a while, and because they get stuck in between one’s teeth. The fact that one ate cheese after meat will not remove the meat taste, remove the leftover meat from between his teeth. Therefore the person that ate both types has to now wait, because of each type.