I followed the tutorial creating the same object. What I got was weirdness.
See 4 screen shots.

click to view larger.
Number 1 screen shot: Round bottom brown shape with 2 width black line.
Crown above it was yellow - it had a line around it, but I un-enabled it. I used the DELETE EDGE tool to remove the bottom of the crown.
Number 2 screen shot: Welded right bottom point to right side of round shape. Bottom shape turned yellow - everything got a thick black line around it.
Number 3 screen shot: welded left bottom point of crown to bottom round shape. Everything is now yellow with thick black line. Note brown section in bottom yellow shape.
Number 4 screen shot: I added bones and moved everything back and forth. Brown shape moved and grew....note how bottom of brown shape makes a directly line from two points of crown I welded on.
Try Tutorial 2.1 and see if you get different results. Maybe I did something wrong. I tried it with welding with lots of shapes and got lots of really strange results. Is this a bug, normal or new feature???