Hello! Nice mod. :)

When a tile blueprint is placed on top of water, a landfill tile and and a ground tile will overlap the same space. In this scenario, shooting a landfillable tile without landfill in your inventory will shoot ground tiles anyways and void them.

• Without landfill, tiles which can't be placed yet will fly out of the gun and into the water pool, getting voided.
• With landfill, bricks will still fly out of the gun; however, landfill tiles will not be prioritized over ground tiles like bots do. The landfill tends to fly out eventually, but will occasionally scatter on the ground as items.

I tested this with a few smaller patches of water generated by Alien Biomes (see https://files.catbox.moe/1ou253.png for image).

Are you using the latest version of the mod? I know that was a problem several versions ago, and I'm unable to reproduce this with 0.2.11. It won't shoot without landfill in my inventory and it won't shoot bricks into the water before landfill gets placed

Maybe it's something about alien biomes specifically if that's not the case.

I am now running version 0.2.13 on a moderately-sized mod list. Upon further investigation, hovering over ghost tiles revealed that they're affected by a few of the planet mods I've tossed in. So I toggled various planet mods, and was able to reproduce the bug with just the Cerys mod toggled.

This bug can be reproduced with Cerys, its dependent mods, and Blueprint Shotgun enabled. This was tested on the latest version of these mods as of writing. (It lists the Blueprint Manipulation Library as a dependency, although with this dependency by itself, the bug does not happen.)

Here's a link to the mod: https://mods.factorio.com/mod/Cerys-Moon-of-Fulgora