Hi,
I\'ve seen this too.
To be precise; the correct mass is not incorrectly reported, but the incorrect mass is reported correctly. What I mean is that this is a bug in the code to add or remove blocks (where the ship\'s mass isn\'t updated properly), and not a bug in the code to display/report a ship\'s mass. If someone figured out the exact conditions that cause this bug, it could probably be exploited (e.g. by removing and re-adding blocks to create a very light cap-ship that has much better thrust and is also much cheaper to buy from catalogue).
I encourage everyone to try to figure out how to exploit this bug, as it\'d be much much easier for Schema to fix the problem if the exact conditions were discovered. It could be that the game subtracts too much from mass when blocks are removed, or that the game fails to add enough to mass when blocks are added, or something else. It might also depend on if the symmetry tool is being used or have other pre-conditions.
There\'s also a different/unrelated bug, where the mass being displayed isn\'t updated while you\'re in build mode if the ship is docked. Undocking fixes this (and therefore I don\'t think this bug can be exploited). However; this could also be a pre-condition for the \"mass calculated wrong\" bug (e.g. maybe loging out after adding blocks to a docked ship causes mass to be saved wrong or something - I don\'t know).