Hey-Hey!!!,
Don't worry about the warning, it's an artifact of the electrical FEA. It wouldn't happen in real life, the CCS would just saturate at low voltages.Also, the overshoot is a result of turning the system 'ON' with the tubes heated up( it's valid for SS and Hg-vapour models ). With a slowly heating cathode, there is none of that sort of overshoot with L-C filters.
cheers,
Douglas