Certainly the first glitch is something I haven't been able to reproduce,and I honestly don't know the exact conditions and the skills I used to get it...I was merely chaotically clicking with the builder icon and suddenly it happened.The lemming went up really fast,I can say as fast as a lemming falls down or even faster.
I can tell you more about the second glitch:
I put a blocker on top of terrain which is covering (working) lava.The blocker was holding off the crowd to go to the right and then I blew up the blocker.Instead of going into the pit,which had uncovered a bit of lava,the lemmings still turned around.
I built into "it" to see if it would reflect my builder,and it didn't.After a few bricks (2 or 3) the crowd headed into the lava pit.
As for the builder thing,I might have built over "it" instead of trough"it" but it certainly didn't look that way.
As I've noticed this before in the vicinity of steel areas,I have a little theory that the blocker's forcefield doesn't dissipate after blowing up,when it is in the range of an interactive object or steel area.
Both glitches were encountered when using CustLemm.
I'll try to reproduce these things and provide screenshots if I'm fast enough