Even if you averaged those values, you wouldn't get 12.07.
There is nothing outrageous or crazy about this problem. By definition (not correcting for activities), pH = -log[H+], and mathematically, proton concentration greater than 1M will give you a negative pH. By the same reasoning, hydroxide concentration greater than 1M will give you >14 pH. Of course, you probably will not be able to easily measure pH in this range with your electrode, especially considering that the calculated pH and actual pH will be different due to ionic strength, and that electrodes are usually calibrated to ranges closer to 7 (typically 4, 7, and 10). But as a theoretical calculation problem, there is nothing wrong with this problem or the answer. Remember, math never lies, if it is applied correctly.