Your landmine thrower is not replacing landmines for the same type that was previously there.

I setup a creative mod server, I used the mod https://mods.factorio.com/mod/Slow_mine
I configured 2x of your guns, each being stocked with a different land mine type.
I then placed two rows of landmine, each row being a different type.
After a biter wave was killed by the land mines and your guns replaced the landmines and I ended up with a mix of landmines.
see this screen shot .. https://imgur.com/a/AarLsaf

It's not a bug per se. Turrets shoot at flares of the same category, but they themselves can only have one category. To have turrets only shoot at specific mines, there would have to be a different turret type for each land mine. I decided to just make it all one category, which also would allow players to "upgrade" to a new type of land mine, but as you can see it can result in mixing. If there's interest though I could try making "damage" and "status" categories so that you can stock slow and normal land mines at the same time.

That would be cool. Basically I have slowdown mine the farthest out from my 1st wall, then explosive ones a bit closer. You mod is fantastic though and is so much better than using bots. So, beggars can't be choosers lol.

This mod has 5x additional types
https://mods.factorio.com/mod/SchallLandMine

But he also has his own mod for deploying mines remotely and as you pointed out there is a gun for each landmine type
https://mods.factorio.com/mod/SchallArtillery