Crashes have been narrowed down to the merge tunnel block, the passage isnt reporting issues.

I've noticed today that the Large tunnels are completely air-tight as if they were a solid block, preventing air transfer between both sides of the tunnel and making the space between a vacuum. This appears to be a function of its current mounting points being a solid cube, assuming you haven't manually set the IsAirTight flag to True.

The block will need the following block of text in its Definition, according to my tests in Debugging mode:

<MountPoints>
<MountPoint Side="Left" StartX="0" StartY="0" EndX="1" EndY="0.2" />
<MountPoint Side="Left" StartX="0" StartY="0.2" EndX="0.2" EndY="0.8" />
<MountPoint Side="Left" StartX="0.8" StartY="0.2" EndX="1" EndY="0.8" />
<MountPoint Side="Left" StartX="0" StartY="0.8" EndX="1" EndY="1" />
<MountPoint Side="Right" StartX="0" StartY="0" EndX="1" EndY="0.2" />
<MountPoint Side="Right" StartX="0" StartY="0.2" EndX="0.2" EndY="0.8" />
<MountPoint Side="Right" StartX="0.8" StartY="0.2" EndX="1" EndY="0.8" />
<MountPoint Side="Right" StartX="0" StartY="0.8" EndX="1" EndY="1" />
<MountPoint Side="Top" StartX="0" StartY="0" EndX="1" EndY="1" />
<MountPoint Side="Bottom" StartX="0" StartY="0" EndX="1" EndY="1" />
<MountPoint Side="Front" StartX="0" StartY="0" EndX="1" EndY="1" />
<MountPoint Side="Back" StartX="0" StartY="0" EndX="1" EndY="1" />
</MountPoints>

This should, in effect, give a hollow box lacking mounting points on both front and back (defined as Left and Right, respectively) while still allowing the tunnel to be mounted against other blocks and preserving air-tightness to the outside when connected with another tunnel.

The Large Passage blocks are similar, but I didn't go into examining their mounting points yet. Small tunnels look fine.

I will look into this when i get chance, thanks for the heads up

So I've just loaded a world I haven't been in for a while. I was using the merge passage. Which now seems to be just a standard passageway. On loading the world it was oriented wrong from how I placed it and it doesn't function as a merge block at all anymore. This seems to be completely broken now.

When was the world last loaded? havn't updated the block in a while. Also is it just that old world or does it do this on new worlds?