This is a property of those symbols, standard behavior on the SS5 trees.

This setting is often configured for symbols that you may want to place along another entities, but should not go in the middle of the other entity, such as a alley of trees along a road (or in a dungeon, torches on a wall). It allows you to easily make sure all of the entities have the same distance from the centerline of the target entity.

The reason you don't see it every time you place a tree is that it is only triggered if you actually align the tree to something else. If it is placed in free empty space, there is nothing to align to, so this step will be skipped. To force this behaviour, when placing trees, move your cursor over a line/poly entity in your map, such as a road. You'll notice that once your cursor is over the center line of the road, the tree will rotate itself to align with the road ("aligning" for a tree may not be very obvious, but you'll see it rotate anyway), and if you click to place when it is in this state, you will get the Offset behavior.

If it just seems to happen out of the blue, for example in an empty area, there probably is a line or edge of a poly hidden on a sheet behind there somewhere. Even if you can't see it, CC3+ will detect it.

I have a macro that draws one here, if you can use that as a base:

You can change the scaling of the fill.

If you click the FS indicator on your status bar to get to the fill style dialog, go to the bitmap files tab, and pick the relevant fill in the dropdown, you can change the values under "scaled" to change the size. Larger size means less tiling, but remember that the resolution of these fills aren't infinite, so they will appear pixelated if you set this too large.

You can just pick a different drawing styles from the :CC2DRAWTOOLS: window.

But you will need to import the fills first, have a look at this FAQ topic.

Thanks, that completes this set.

According to the count, there are now 1099 maps in the atlas. No need to go out and hurry to make the 1100th one though, I still have maps in queue for processing.