Exceeding of state vector

[Charles Yin]

Hello everyone,
I have encountered with a problem of state vector.
The state vector in OpenSim has the form of x=[q, \dot{q}, a(0), l^M(0), a(1), l^M(1),..., a(n), l^M(n)]^T, whose names can be obtained by 'OpenSim::Component::getStateVariableNames()'. While, from 'SimTK::State::getY()' we can also get the continuous states variables.
In most cases, the number of states is equal to the continuous states variables. But when I added a bushing force into the model, the continuous states variables have one more than states.
I know that bushing force is a function of generalized coordinates q and velocities \dot{q}, and now I just want to make them consistent in size.
Is there any advice for adding bushing force (or other variables) into the state vector? I propose this question mainly based on 'OpenSimPlantFunction.m' from the resources 'DynamicWalkingStarter'.
Thanks for your attention and support.

-Charles