Just to make sure, that I understand you proposal correctly. You want the following behavior:
1) Brick 1 adds pixels and brick 2 adds pixels: Don't change anything, i.e. use the current checks.
2) Brick 1 adds pixels, but brick 2 does not: Place two bricks and turn after placing the second brick, i.e. the current behavior.
3) Brick 1 does not add pixels, but brick 2 does: Behave like in case 1), i.e. ignore the problem with the first brick.
4) Neither brick 1 nor brick 2 adds any pixels: Turn around after placing the first brick, i.e. the current behavior.
Correct?
Except for #2 (in this case, the lemming would place
one brick then turn around), this is actually exactly how the stacker behaves in the stable version.
Nepster mentioned in chat that, basically, the changes were to bring stacker behaviour more in line with Platformer and Builder behaviour; the most obvious thing that was different before (to an end user) being that builder and platformer have no special treatment for the first brick.
The reason Stackers did, originally, is because not doing so would make it impossible to stack properly on a 45 degree upwards slope, which would be somewhat crippling to the skill, not to mention very annoying on rough-edged graphic sets.
Ultimately, as I usually do for physics these days, I'll defer to Nepster's judgement on this one, but I felt it was important to explain
why the old rule was what it was.