I found a few bugs...
1 - It calls a setSize function that doesn't exist anymore but I don't *think* it is needed -or- it needs to be added back. Need to do some tests.
2 - When expanding a pool, it shows all the drives even if they are part of the pool. This shouldn't be a problem to fix.
3 - In a z1-pool, it forces you to expand by at least 3 drives. This also shouldn't be a problem to fix.
So, when you tried again, the first drive was probably already partially added to the zpool. I will try to fix these things in the next few days.