Sascha Alexander Jopen <jopen@informatik.uni-bonn.de> found this.

txParams->duration = Time (m_period * m_dutyCycle);

where m_period is Time and m_dutyCycle is double. Conversion to int -> zero (or m_period iff m_dutyCycle is exactly one).

The line above should be:
txParams->duration = Time (m_period.GetTimeStep () * m_dutyCycle);