When standing on a block and shrinking to a scale of less than 0.0000015, the player falls through the block below them. If they fall or teleport onto the block after shrinking they won't fall through.

Falling through a solid block after shrinking.

Falling through glass. My coordinates are 64.99633, screenshot taken about 30 seconds after I started falling.

Coordinates after teleporting to 0.001 blocks above the glass and landing on the surface.

All the bugs I've found for now ;-)