Hi,
I'd like to mention a bug that lets you walk through Vanilla Iron Bars. All you need to do is to place Irons Bars on any block and then stand on the same block, then if you morph into something, e.g. into cow you'll be standing inside those Irons Bars and you can freely walk through them or just walk inside them.
I think this may also work with Fences but I haven't tried it.

That's vanilla behavior designed to prevent the player from getting stuck in a block. Once you walk out of the fence/iron bars, you should collide with them normally again.

Hey there!
I have to say that this is a serious bug... Players can walk through barriers, doors and world borders, while standing in corner and morping as mentioned.

You don't need to stand in the corner to get through doors, but you need so if you want to get through walls that are 1 block wide (maybe you could walk even through wider walls but I wasn't able to do that).

Fair point @Jason505. In that case, the most reliable solution would be to prevent morphing in those cases.

https://github.com/asanetargoss/metamorph/releases/tag/beta_1.1.6_hitbox-clip-fix

^ Please try the temporary download above for your respective version (1.10 or 1.12) and let me know if it doesn't fix your issue.

Edit: Linked download removed. The fix is now included in Metamorph 1.1.7