I fixed the bug that was producing the error when moving the floating box and updated the link to the new mod here:
As for the objects being destroyed, if they are labelled as ‘clutter’ as most plants are, then they will be destroyed when their supporting block is removed. This was to prevent spam of random clutter when mining the ground, but doesn’t make much sense when you’ve placed them on a structure for decoration. We’ll have to look into this further to find a better solution.