Two items. First the weight for the chassis is being calculated wrong. It appears to be adding in the extra weight for the first mp instead of it being free. This throws off the weight of all designs and shows some as being overweight. This includes IS and Clan.
Also, as per TM the weight of Clan chassis can be chosen to base on IS or Clan designed. Intentional or bug? Not sure how this is meant to work in MML.
The issue with chassis weight being wrong because of not considering free MP was fixed a while ago and this ticket wasn't closed.