Found quite early on but don't think too many cared about it as copy pasting reactor does not happen that often.
You can't copy paste or put specified chambers in a template form and expect it to be placed next time. As the game does not allow you to place down specific chamber block types manually, it doesn't do it either through templates.
Instead, it should just put down the general chamber block instead as in this case the reactor size and shape is much more important to keep than the tree itself.