Other item keeping mods being Ender IO's soulbound enchantment and Tinkers' Construct soulbound tools (I don't know if there are any other mods that can keep items after death).

If you have any anchored items in the first slot (or for first few slots) of your hotbar, they will get replaced after you respawn by other soulbound items.

Pretty easy to reproduce:

1. Put an anchored item in your first hotbar slot
2. Put a soulbound item (Ender IO enchanted item or Tinkers' Construct tool with a nether star) anywhere in your hotbar or inventory, doesn't matter.
3. Die however you like.
4. Soulbound item / tool moves to second inventory slot.
5. Respawn.
6. Soulbound item moves to the first slot on your hotbar, overwriting whatever was there.