I've encountered a bug in the sub editor with duct blocks and their gap placement. I'm using BTE 6.1, and when I place a duct block, the gap only allows water movement sideways, not vertically. Extending of the gap, deleting it, letting it be regenerated upon load does nothing. I loaded the (BTE) Nehelannia II to see what I was doing wrong, but those duct blocks had the right size gap. Upon deletion and replacement of one of the Nehelannia's duct block, the same bug happened where the generated gap would only allow passage of water horizontally, not vertically.