To make:

• Build an uphill track, include some power or detector rails.
• Place a minecart on the slope, over either of those types of rails, when they're in the powered state.
• It glitches through. When it reaches flat ground, it's sunken into the ground, still attached to the track.

Note; the rails with the problem have very low hitboxes. Not sure if that's at all related.

(this is not the minecart-sinking-into-the-ground-when-derails bug; it started happening with the new minecart physics.)