[JeffTheRef]

you correctly, is that there is a block, and that, once the block occurs and the ball is not released, the try ends - thus team control is never relinquished and we have backcourt.

I like it. It serves the greater good of not allowing rules to have unintended consequences.

Your thinking has a nice parallel in the way 'catching the tap' was handled in high school, at least until last year! You caught the tap, you gained possession - thus Team B got the arrow; then you were in violation by virtue of having caught the tap, and Team B got the ball. Even though there is some compelling logic to this, the committee trashed it to make the outcome (you lose the ball, get the arrow) parallel with other situations, and, perhaps, less onerous to one team.