[ld1305]

I've encountered an issue when joining blocks together whereby I seem to have two different edges sharing two vertices, so I'm getting mismatched node counts.

I think it's come from how I've joined them and then merged some vertices to edges, but I'm not sure how I'd go about merging the two edges into one so that it appears as I'd initially intended.

I've attached an image of the blocking with node counts and vertex numbers visible to show that there are only two vertices for the two edges, plus a clearer diagram of what I'm seeing with regards to the counts. Each block appears fine within itself, but where the yellow block and the blue block are connected, they seem to have separate edges between the two vertices.

[ld1305]

It seems like this is less likely to happen if the yellow and green blocks are already sharing vertices at either end of the blue block before merging the centre vertex to the ends, though I'm still not sure how I'm to fix those that are already broken.