Parts should remember if they were added via symmetry. Currently, removing a part that has been added via symmetry and moving it causes the symmetrical parts to dissappear. Adding a part to a symmetrically added part should add them symmetrically by default. Parts that are successfully added symmetrically should be added symmetrically. In large builds, it gets exceedingly frustrating to check that struts are connecting on all parts. Stopping the build process to focus, rotate and ensure that the program does what its told is a time sink. You need to implement double axis symmetry in plane mode, because this is the only place you can build lifters and they need four legs. Two sets of two leads to all kinds of needless micromanagement of stages and difficulties in manually balancing that should not exist. Also, parts that are added symmetrically don't necessarily end up in the same group, leading to morestill micromanagement of stages.