in the old days, this was achievable but very difficult, it was much easier in DOS to place the blocker such that everyone continues upward [follows builder]. This, the former (current Lix) behavior was very unexpected to me, and apparently to others, I remember geoo being stuck on the level
"Final Call" by BulletRide
for a very long time by his standards, which utilizes this very behavior.
At some point in SuperLemmini's existence, this was the standard and I don't believe lemmings following the builder up was possible.
I personally vote for the latter behavior; letting lemmings follow the builder. It seems much more natural than the former. level was the only one I've ever heard of to use this behavior.
The former behavior should either be an option or left out entirely. It does have uses but more behaviors lead to more confusion etc.