It isn't unusual when it's a brand new technological generation of stock. The whole metro/tram industry is still in-transition to a generation of rolling stock that is now stacked to the extreme with software-based control systems. In contrast the most recent subway stock the T purchased, the Blue Line 0700's, had relatively simple and task-limited computers with a lot of remaining analog electrical or electromechanical controls decidedly old and resource-intensive to produce as parts. Believe it or not, with a finalized design year of 2004 (15:!: years ago) for '07-09 delivery, their tiny brains are already 1-1/2 decades old. The computer complexity on the Orange/Red cars and even the Green Line Type 9's is light years ahead of that, with firmware programming absorbing far greater share of all of the train's various control systems than their much simpler predecessors.
New York and other systems have had similarly sluggish and/or painful adoption of its new-gen cars as they get over the hump on all these new layers of software debugging. The good news is that once replacement procurements have sufficiently flushed the railcar industry onto this new tech generational leap the follow-on orders get MUCH easier from here on out and build off the coding bug fixes the first-wave buyers implemented. If we're buying off-shelf trolleys for Green Line Transformation, then the pain and suffering other systems did/are going through debugging the latest-gen reference models will pay off by giving the T a much easier time piggybacking. When Buy America imposes its own world of hurt on delays and cost overruns, that's not at all insignificant a boost.