Yes, they seem a bit fishy.
I think I've discovered what's going on with my setup which is that the solar controller has not been wired in typical fashion.
When we look at the wiring on the reverse side:
The black sheathed wires on the top left are from the solar panel and go into the back of the solar controller. 3 Wires exit the controller, 2 neutral and 1 live. The live goes to a splitter with 2 fuses ( only 1 shown in the picture) then on to the master switch on the main control panel which has 3 positions - OFF, hab & vehicle. 1 live goes to the vehicle side of the switch and the other to the hab. When on hook-up the position of this switch determines which batteries get the benefit of the on-board charger.
On 12v, when the hab fuse is pulled like in the picture above B1, which is the leisure battery circuit, shows a fault.
This is simulating what is happening when the engine is started. Wiring the solar output to the master switch works OK for the engine battery because there is always continuity but not for the habitation side because it's isolated by a relay when the engine is running (I think).
What I need to do is disconnect the solar live from the hab side of the master switch and route it through to the leisure battery under the driver's seat. Not an easy task and something that I will have to ask about on the Autosleepers owners forum.