I even remember Shvegait labelling level 4 "glitches galore". Though my solution leaves the digger, so perhaps I should look for a glitch free solution as well.
Level 9 is borderline, as there's no really glitchy behaviour per se, but it's difficult enough to pull off that one might expect it not to work at all.
I'll send you the link to my solutions via PM.
For the record, I don't need the pausing trick at the start either, but it makes levels 2 and 3 a bit easier.
EDIT: I find it really interesting that both me and ccexplore found level 6 the hardest, and now I see it's also on Clam's unsolved list, but when looking at the solution after I finally found it, neither of us could really pinpoint the element that made this solution so hard to figure.