Setting the units system breaks DC power flow in an alarming way

[GabrielKS]

The voltage angle is corrupted when running a DC power flow on a system with units base system set to natural units: which makes one wonder how much trust one can put in other PowerFlows outputs, even when they're not as outrageous as this…

[jd-lara]

this is weird. I think we need to implement a check to solve the PF in Per unit. I don't even know how can this converge on natural units.