To copying pieces:
That copied pieces spawn a bit below the original can lead to the problem that they spawn outside of the reachable map if the original is too low on the screen edge. You can still reach them by increasing the lower map size though.
One idea against that problem would be that tiles are spawned above the original tile iff they would end up below the map border.
I think this issue is still not in github but it came up again in IRC:
16:20:12] <Ramond__> maybe an editor suggestion
[16:20:30] <Ramond__> cloning tiles that are aligned to the bottom of the map should not clone downwards, only sidewards
[16:21:15] <SimonN> right
[16:21:39] <Ramond__> perhaps something analogous for right-bound tiles
[16:22:08] <SimonN> if things would clone to outside of the map, they should clone in the opposite direction.
[16:22:18] <Ramond__> yeah something like that
[16:23:20] <SimonN> Also game should remember where you moved after cloning, and clone the next stuff again in that direciton.
[16:24:55] <SimonN> To aid building long walls/floors from a sequence of the same tiles
[16:25:16] <Ramond__> makes sense
[16:25:57] <SimonN> Do you have a github account? You can file issues directly there. Otherwise I'll file it once I remember it. It's also dug in a thread on LF.