Hi Daniel,
Your vehicle is definitely atypical. This isn't a bug. However, it's pretty easy to get around. You can hack SUAVE to do this without changing the source.
You can add a function to your script and have the mission call that function instead. Here's the function:
def initialize_weights(segment):
m_initial = segment.analyses.weights.vehicle.mass_properties.takeoff
segment.state.conditions.weights.total_mass[:,:] = m_initial
When you setup your mission just add this line to the segment you want the weight to change at:
segment.process.iterate.initials.weight = initialize_weights
-Emilio