Just want to explain what causes the weird offsets (floating trees, or ones dug into the ground) again.
Offsets should be consistent between all schematics. Oak has a different offset from cottonwood and from poplar for instance. The 'ground' should be on the same height in all schems tho. Ideally, they should all just start from the ground (I don't think we do roots anymore do we?)
The problem - as far as I understand it - is, that we were anything but consistent in the way we set up schematics.
Think of a schematic like you making a WE selection, copying that selection into your clipboard and then pasting it elsewhere, only that the content you saved into your clipboard is stored as a schematic file on the server, and you can call that file later and get the selection into your clipboard to paste somewhere. That's what the schematic brush does when you select a Set of schematics (the SchemSet): it randomly selects a schematic file out of a predefined list of schematics, waits till you pasted it, then selects another one, etc.
Any Editor can set up a schematic, and make a set of several schematics. We have never established detailed guidelines for setting up these thing, which not only lead to all sorts of strange names for the sets, but also inconsistently set up schematic files. This means that some people selected the object they wanted to store as a schematic and tried to limit excessive, empty area so there is no empty blocks below or above the object, e.g. a tree. And others didn't pay attention to that, and there are excessive air blocks above or below the object. This can be fixed by declaring an offset when making the set, so that every schematic in the set is placed a couple of blocks lower, for instance.
The issues arise when we mix differently set up schematics inside the same set: imagine a number of oak trees that all have 2 blocks of air underneath, and a number of elm trees that don't. If you were to make a set out of these, you cannot fix the offset of the one species without altering the behaviour of the other.
Tham has re-defined a number of schematics to work with his forest scripts. The way he set them up, they do not have any excessive air blocks below or above. Some of these re-definitions changed the behaviour of species used in mixed sets, which now reference schematics that are both fixed, and schematics that are not fixed, because the set was declared with certain offsets.
This can - in theory- be fixed by adding -place:<PLACEMENT>, where PLACEMENT is either CENTER, BOTTOM or DROP. In most circumstances you would add -place: DROP, which supposedly places the
lowest nonempty block of the schematic
on top of the block you clicked. Unfortunatelly, the brush does not seem to actually do that, which might be a bug in the schematic brush.
The solution to this is to set up all schematics in a structured, organised and uniform way, and to do so in the future, and then to redefine the schematic sets.