I would say both of those phenomena fall under the category of obscure (or familiar, for some
) game mechanics. For example, the digger+blocker combo simply takes advantage of the fact that a digger only needs one pixel under him to keep digging, and it can be on his extreme left or right (actually, the pixel doesn't even have to be under the digger of course; the "digger field" extends one pixel beyond his feet on both sides), whereas a blocker needs a couple pixels of terrain directly under his feet to remain a blocker.
The second "glitch" is similarly dependent on subtle (albeit probably intentional) game mechanics. If a digger has no terrain under him within his "field", he stops digging, and a second digger can create this situation quite easily.
Doubtless, however, these are both very useful mechanics for us level authors to take advantage of