What the heck happened on the Orange Line this morning?!

It's the kind of temporary flukey stuff that if you don't document it, people (including the T itself) will swear never happened. My usual train inbound to North Station, the 7:24 from Chelsea that likes to come at 7:26 and not leave 'til 7:28, arrived at 7:42 as usual (7:38 when it's on-time). I actually managed to be second in line off the car I was in, giving me the advantage of getting to North Station-Rapid Transit quicker and actually making the 7:46 to Oak Grove instead of having to wait for the 7:51, meaning that I had a decent shot of making the 7:50 employee shuttle out of Sullivan Square. But no! The train pulls in as I'm going through the turnstile and I bolt for it, figuring that, as it should, it will unload, load then leave ASAP--instead we sit for a painfully long 30-something seconds (precious time considering my connection). The same things happens at Community College. Thus, the train lost at least a minute getting to Sullivan Square (we arrive at approximately 7:49:50) and, as my connection was right on time for a change, I had to wait 'til 8:00 am.
But that's me. An even better story is what happened to a colleague of mine 15 minutes earlier. He was on the inbound train just before mine, which does run on time, makes the stop at Chelsea at 7:06--although usually runs early for 7:04--and gets to North Station between 7:16 and 7:18. Thus, he would have caught an Orange Line Oak Grove train by 7:25 at the latest. Yet , he didn't get to Sullivan until 7:55--after me! Here's the explanation:
Apparently the T was doing some secret, undisclosed, whatever-you-want-to-call-it track work or train routing on the Orange Line morning around the time he got on, which apparently was done by the time I got on. He said that the train left North Station, then announced it was going express to Wellington, i.e. not stopping at Community College or Sullivan Square! So, he and other uninformed passengers bound for stops in between were forced to go to Wellington and then take a southbound train. Unfortunately, there hadn't been a train in the southbound direction in quite some time so by the time he made it up to Wellington and tried to get the first train back, he couldn't--it was that packed! He managed to squeeze on the next one (presumably also packed) and thus got to Sullivan Square after me! So what happened? I guess trains were being sent express north to make up for the southbound deficit--the question is what happend up north? Area trackwork and signal work is supposed to be after-hours and on weekends. And don't tell me it's because the Boston Public Schools just started today--these are communities north of Boston!