Good find with the inconsistencies. Looks like we stumble on these things afresh because we haven't seen them in 7 years. Design history of the buttons:
Around 2007 or 2008, C++ Lix got vertical flip and rotate. I chose vertical flip instead of horizontal mirroring because I forsaw compatibility with L1 as useful. Accordingly, I made f the notation for vertical flip in the file format.
I already had the tree as the symbol to add terrain, and re-used the tree for the icons of the vertical-flipping and rotating buttons.
Around 2008 to 2009, two things happened, and I've forgotten their order. I added horizontal mirroring because that's more useful than vertical mirroring. And to support the L1 format fully, I added eraser pieces (a.k.a. dark) and no-overwrite.
It's hard to recognize the tree icon from its horizontal mirror image, and therefore the 3 new buttons -- horizontal mirror, eraser piece, no-overwrite -- got more abstract tiles in their illustrations. But I didn't remove the tree from the earlier buttons, it was too clear an illustration. Everybody knows where a tree should have its stem.
Yeah, the zoom lens would be my first attacking target when it comes to designing the panel. Maybe some buttons can shrink and others stay as they are, hmm.
I'm pondering to add visible grid lines to the editor. I imagine those need a button, too. Thus, bigger UI revamps aren't entirely off the table. Keep the ideas coming!
-- Simon