Why does the colllector current decrese with decreasing collector-emitter voltage in this circuit?
In the top simulation, your \$I_c\$ is only changing by 10uA for a 20mV. This is just the effect of the Early voltage and the finite output resistance of the transistor. From your data I calculate an Early voltage of about 80 V (very reasonable). I don't know what's going on with the LC tank, but it isn't the cause of the \$I_c\$ variation.