JK Flip Flop toggle action
simulate this circuit &ndash; Schematic created using CircuitLab


For example When both J=K=1; the input NOR gate-1 &amp; 2 respectively 0 &amp; 1.When one of the input of Nor gate is one the output will be zero.so when Nor gate-2 output change to zero then both input of NOR gate-1 will be zero so output of NOR gate-1 changed to one.As per your point of view both q &amp; q bar zero may happen between toggle states (I mean it may happen @ time between NOR gate-1 take Q bar=0 output &amp; changed NOR gate-1 output equal to zero).But stable final output will be toggle one.
Sorry friend if any wrong in my logic.Kindly please let me know if any..