Incorrect ODE replacement when if-else block exists with derivimplicit method

[pramodk]

If we have derivative block with derivimplicit method like :

DERIVATIVE states {
    IF (tau_m<taumin) {
        tau_m = taumin
    }
    m' = (m_inf-m)/tau_m
}

The SympySolver generates :

DERIVATIVE states {
    IF (tau_m<taumin) {
        LOCAL tmp_m_old
        tau_m = taumin
        {
            X[0] = m
        }{
            tmp_m_old = m
            m = (dt*m_inf+tau_m*tmp_m_old)/(dt+tau_m)
        }{
            m = X[0]
        }
    }
    m' = (m_inf-m)/tau_m
}

This is because I thought it's good idea to track last statement block and then inset statement there. But as we can see, it fails in above case as if's statement block gets used.