Simply put, repair blocks vanish when flowing water (such as from a destroyed vanilla village garden) runs through it. Is there some way to make the Repair placeholder ignore flowing water (or all non-source fluids)?

Yeah I recall having this mentioned to me and looking into it, I guess I hadn't quite solved the problem, might be able to tackle this soon, really need to fix it without breaking the ability for you to place into a block manually to wall up an area in a hurry.

A similar issue, perhaps slightly different, regarding repair blocks never appearing to replace any block which does not fill the entire square: fences, stairs, tilled dirt, grass_path.