Looks like I found a remedy (which may also indicate where the error is):
1. Create RAIDs one at a time, finish after each one.
2. It says "Starting the partitioner" (apparently it writes and rereads tables)
3. Select "Configure SW RAID", etc.
Takes more time (each "Starting ..." takes a minute) but apparently works fine.
Looks like I found a remedy (which may also indicate where the error is):
1. Create RAIDs one at a time, finish after each one.
2. It says "Starting the partitioner" (apparently it writes and rereads tables)
3. Select "Configure SW RAID", etc.
Takes more time (each "Starting ..." takes a minute) but apparently works fine.