Production of items for a higher level Black-tree with lower level Black-tree
The Black-trees can produce a higher level buff than the tree actually has.
As long as you have one tree at level 7 the other trees with another colour can stay level 1.
https://i.imgur.com/gKlxNpm.png
Black-tree (blue) level 7.
https://i.imgur.com/sG3COsu.png
Black-tree (gold) level 4.
When you 1st click on the level 7 Black-tree (blue) and then without closing the window of the gold tree, click on the blue tree you will get
a level 7 production line in the level 4 window.
https://i.imgur.com/ixKmNa1.png
Black-tree (gold) level 4 with level 7 production line.
https://i.imgur.com/i5y0hpB.png
Black-tree (gold) level 4 with level 7 production line. Selecting the Black-tree Arrow.
https://i.imgur.com/cisVqU7.png
Black-tree (gold) level 4 with level 7 production line. Producing the Black-tree Arrow
So if this stays as it is, you have in the future only need of one level 7 tree, all the other colour trees can stay level 1.
Interaction of production buildings that should not be.
The real problem is that you can select another building wile the production line of the last building stays visible and accessibel.
Take for instance Adventure Book-builder and Oil Mill.
https://i.imgur.com/1gp5jU8.png
https://i.imgur.com/UUxiCeO.png
If first you click on the Oil Mill and then click on Adventure Book-builder you wil see that the Oil Mill production line stays visible.
https://i.imgur.com/csipIju.png
You can even select the production
https://i.imgur.com/Bzw20HO.png
Pressing the green button will let the game crash. So production is not possible.
https://i.imgur.com/yGLiOOF.png
Other buildings can give strange production lines too, such as books in the Chocolatier.
https://i.imgur.com/inH9kVs.png