Hi Karen,
When you are weaving double weave on 4 shafts, you will get a horizontal join whenever you change from an A Block to a B block, or when you change from a B block to an A block because you are lifting what was on the bottom to now become the top layer. Then as you continue with the same block you will get a tube for the length of that block. When you switch back to the other block the two layers will close up again.
Is this the stitching together that you are experiencing? Or are you getting the layers joining together through the whole block?
Weaving Block B, it is treadle 5 (T) which lifts shaft 2;
treadles 1 and 4 (B) which lifts shafts 1, 2 and 4, (shafts 2 and 4 are the top layer lifted out of the way, and shaft 1 is the first half of the plain weave for the bottom layer):
treadle 6(T) which lifts shaft 4;
and finally treadles 2 and 4 (B) which lifts shafts 2, 3 and 4. (shafts 2 and 4 are the top layer lifted out of the way, and shaft 3 is the second half of the plain weave for the bottom layer)
It looks like you are weaving Block B correctly, so if the B tube is being stitched together throughout the block, check to see if there are threads crossing at the reed.
let me know if this helps, or if there is something else going on.