A known issue is that one or more ghosts become duplicated. I haven't found out how to replicate this. If someone has a way to reliably replicate this I would like to know how it happend and the save in which it is easibly replicatable

Still need how to replicate duplicate ghost issue ?
I think i know how.

yes please

OK, i test this by only using TMG mod and nothing else, with Factorio 0.17.42
Also, just in case it's matter, i also unset / delete keyboard shortcut entry of TMG in game control settings option.
Everything else, as far as i can tell is still default.

The culprit was the entity that can be placed automatically when building by dragging.
a.k.a vanilla drag-build feature, with :
-Underground belt
-Underground Pipe
-Electric Pole

Just drag-build that entity over the top any blueprint (with TMG On), you will have a duplicated ghost.

There is however a quirkiness with railway curved track.
Not sure if i can word this out, it's hard to describe....
I'm gonna post video with this specific 2nd case in the bottom of this post.

Curved track is more sensitive / prone to duplicated ghost.
The culprit entity doesn't have to be drag-build to trigger it, just place a single click will trigger it.
Straight track is immune with single click trigger (but still affected by drag build trigger)

Furthermore, there is a thing with underground belt, it's not always triggering curved track ghost with single click, sometimes it take multiple times.
I think this has to do with orientation and belt direction, but i'm not sure.

Also, even if it's just a single click, sometmes it will rapidly trying to place an entity.
The sound of mouse click goes "brrrrttttt", and the duplicated ghost will have many layer
(not recorded in the video, i can't replicate, rare happening)

Here's the video of the 2nd case of duplicated ghost trigger.
Note :
Although the video is recorded with many mod activated,
I can assure you i have test this in non mod game (aside from TMG obviously)
I just forget to record the 1st one.

https://youtu.be/EA3HG-LLu10

Thanks, can you also post the save? just in case I need it

It's just a generic (non-modded;vanilla; only TMG) new game.
Sure you need it ?

Hello,
do you need more data to try and fix this ? Also, I feel this in something the engine shouldn't allow, is there a bug report for it in the factorio forum (couldn't find one) ?

I believe I managed to fix the issue with the steps given by kyoshiharu, but if you found a different way to duplicate this, please post. I did make a bug report for overlapping multiple ghosts, but the devs said it was intentional(https://forums.factorio.com/viewtopic.php?f=23&t=55514)

I got this happening in a recent game (latest version) while placing a blueprint, I ended up with some inserter ghost placed multiple times. It wouldn't be too much of a problem though if the mod had let me placed those inserter, but I actually had to delete the excess ghost before I could place anything.

I'll try to see if I can reproduce that and I'll send you a savegame.