placing explosives

I cannot place explosives at certain postitions. There is a unearted remnant, but the circle stays red in every position I try to place the explosive. Specially when there is a wall / open door between the detonator and the remnant.
Can only place exposives in the same room, not when there are obstacles between detonator and remnant...
bug?
(I don't know how to upload a screenshot)
.....


Just found it out....
Must be a line betwen detonator and exposives that are further away.


Solved

Don't think it's a bug. The Kalguurans can only run a line of certain length away from the detonator before placing an explosive (think Redstone Dust electric signal strength from Minecraft). In order to reach the further Remnants, you must first run 1 intermediary explosive to provide enough energy to path to the far Remnant.

Also, only certain terrain is suitable for placing explosives on. It looks like particularly fancy dirt. You cannot place explosives on ground that isn't fancy dirt.

EDIT: Nevermind on the fancy dirt part. Guess I was bamboozled by that.