Yeah, this is clearly Akamatsu's decision. He's provided some of the best work to the magazine to the point that he even gets a week off every month. Which makes it all the more mind boggling because if it were an editorial decision, I would understand.
I mean WHAT was the point of giving Ayaka, Akira and Chizuru their pactios, getting Fate to teach at the school, giving even more wacky side adventures, introducing new magic combos, developing characters that haven't been touched before like Sakurako and Kakizaki (and Madoka seriously needed development) hinting at tons of potential new plot threads like the Demon realm, India, time travel, not to mention ALL the plot threads still left to resolve apart from Nagi, there's still Negi's mother, the secret of the pactio system, the cloaked figure, a ton of character backstories like Misora's, Ako's, Yuuna's, Mana's etcetera, etcetera, just WHAT was the point of all that if he was planning to end this is a few months.
Just a couple of chapters before the end, he was introducing new stuff like it was nothing. Then we get a 5 month timeskip and THIS happened. I just can only come to two conclusions. Either there's going to be a Negima part two with the characters ageified (if only, if only) or he planned to do more but ALL OF A SUDDEN something happened to change his mind and just end things now causing the manga to get the pervasive feeling of unfinished business in the process.
But like I said, he was introducing stuff from two chapters ago, everything felt like he was shifting to a new stage, a final stage but a new one nonetheless. He wouldn't have bothered if he was planning to end it all soon. But alas I'm not that much of a wishful thinker that I would even hope for a part two after the announcement of the manga's end. I just don't have a clue what the hell happened here.