Hello,
if you try to buy echo but drop it in the buy window, it goes to the buy back tab. You can “re-buy” it, but then it goes to your normal inventory instead of the specific tab for them.
I tried to stash then and bring them back to check if they got relocated correctly, but that was not the case. The workaround that worked for me was dropping them (I “bought” another that way just to check if this was in fasct a bug) and then recollecting them back from the floor, then they got stored iun the proper tab that can be used to place them in the map.
Thanks!