Join up to a high ping server (120 and up seems to work) running SVN and 32in24-5 MAP02 (just one of those reproducable maps, its not exclusive to it). Join and run past the BFG and in most cases, the server will never tell the client that it got picked up, thus giving the player an SSG or Pistol that fires BFG shots and uses both cells that the player isn't aware of, as well as using up Pistol or SSG ammo.
This was [re]introduced whenever GhostlyDeath's item pickup code was removed, around revision 1500, if I recall correctly.
I just want to go on record to say that this WAS NOT reintroduced because of the removal of GhostlyDeath's code. Ghostly's item/weapon pickup code did not solve desync problems, it only masked them (barely) and caused many other issues on top of them. Ghostly's approach to this fix is not the answer.
In the meantime, Spleen and others have kicked around the idea of having all pick ups be entirely controlled server side. This is worth trying out.
Dup of 269
*** This bug has been marked as a duplicate of bug 269 ***