In the windows version 0.0.254B. Windows 7 64bit
If you sell a weapon to a trader and then buy it back with out closing the window it drops the weapon of as if you had brought them but your colonist will not interact with them. (wont haul or equip them.) Saving and reloading fixes the problem.
I found this out when I accidentally sold my m-16 to a weapons trader and then immediately brought it back It landed an m-16 as if i had brought one but it my colonist would not interact with it I could tell them to equip it or hall but this did nothing they ignored the order and did not pick it up out of there own accord. I had vacant weapon racks.
I then tested the same sell and then immediately bye back method and was able to reproduce the bug on all weapons.
If I sold a weapon exited the trade screen and then call the ship back to by the weapon it droped normally and was ineradicable.
Thank you very much for reporting.
Known and reported bug.