If you walk from a block that is shorter than a full block to another block that is also shorter than a full block, but taller than the first, you will momentarily glitch into the original into the block you are walking onto.
Reproducing:
1 Place a bed on the ground
2 Place an enchantment table directly next to the bed
3 Attempt to walk from the bed onto the enchantment table.
4 You will glitch down into the enchantment table, then pop back up.
~ Works with any two blocks as long as neither block is a full block, and you are going onto a block with a taller collision box
Linked issues
is duplicated by 8
MC-442
Player sinks into the ground slightly when moving from slab to bed
Resolved
MC-2066
Anvil Glitch. Going from Slab to Anvil, you will glitch down before ending up ontop of the anvil.
Resolved
MC-2460
Bouncing up and down by bed
Resolved
MC-2737
Bed surrounded by half slabs
Resolved
MC-4805
Entity bounce when traversing blocks that have Y sizes in increments other than 0.5.
Resolved
3 more links
I can confirm this bug. I had to fix it for my resizing mod to work properly, after it kept causing "illegal stance" errors in multiplayer.
(Using MCP v7.25 on Minecraft 1.4.6)
The piece of code that needs to be changed is in the Entity.moveEntity method, in the part right before the Profiler section "rest", just before where Entity.ySize gets changed:
double var40 = this.boundingBox.minY - (double)((int)this.boundingBox.minY);
The "(double)(int)" causes the player to glitch through to the bottom of the short block before getting popped back up. My fix was this:
double var40 = this.boundingBox.minY - var29.minY;
Where "var29" was the copy of the entity's bounding box made before checking block collisions:
AxisAlignedBB var29 = this.boundingBox.copy();
I hope this helps 🙂