I've had this same problem. Twice. Both times I had LED and regular diode elements in my circuit. It was the introduction of a third diode into the circuit that caused it to begin happening. Before that I had two diodes and I believe three LED's active in my circuit. Diode D6 (a regular diode) was placed, named, and the Vf was adjusted, and then BAM! Everything haywire and no way to get it to go back to normal no matter what I tried. I ended up having to abandon it and start all over. The second time it happened it was D2, the second diode introduced, D1 was an LED. D2, a standard diode, was dragged in and BAM! I didn't even name it or adjust the forward voltage or even go into the parameters page.

I also get this problem I have a circuit I want to play with but I can't change the leds to use a different amount of current at x voltage you get the point right?

Sorry for the trouble, the diode model has been a tricky one to diagnose. Thanks for your patience.