Please correct me if im wrong

Dropping mines such as Proximity mines and Cluster mines is a "Action"

as oppose to dropping Seismic charge and ion bomb does not require "Action"

Is this correct?

so this scenario is legal

Drop seismic charge, proceed with maneuver, drop cluster mine as action.

It would be legal except there is a clarification in the FAQ that says a ship can only drop one bomb per round.

It also keeps you from using PTL and dropping two bombs on top of each other.

It also keeps you from using PTL and dropping two bombs on top of each other.

You would never have been able to use PtL to drop bombs anyway, as it must be an action from your action bar.