Reproduction steps:

• someone who has a botkiller (can be on either team)
• disguise as them
• mash "Last Disguise" bind with revolver/sapper (primary, secondary if demoman/medic disguise) to cause the game to just create a botkiller attachment that tries to glue itself to your viewmodel.
• the more you mash it, the more botkiller attachment viewmodels are made (these are created on a delay, so they won't show up instantly. seems to be on a roughly 1 second delay?)
• oh by the way, each of these takes up 2 edict slots. so of course...

• swapping disguises clears the botkiller attachments, and frees up the edict slots used.