@Age of Darkness - I found a duping bug causing a clip (default 8) "Tranquilizer Darts" to be created.
Steps to Replicate:
1) Load both ammo types into the gun (10 for example)
2) Swap to regular Tranq Darts (Gun will read 8/10 darts and 10 total darts will be in the inventory---2 should be in the inventory not 10 as 8 are in the gun)
3) Drop remaining inventory of Trang Darts (10 darts will be on the ground, but 8 are still in the chamber)
4) Press "F" to swap to "Shocking Tranquilizer Darts" (the 10 regular darts on the ground are picked up and added to the 8 regular darts in your inventory.)
----the player now has 18 regular tranq darts
It looks like you have addressed this when going from "Shocking Tranquilizer Darts" to regular however, by emptying the clip when they are dropped.

Additional note: After using this above method to duplicate darts, the gun will continue to read 8/XX "Tranquilizer Darts" regardless of which type of dart is equipped, but will consume the correct dart from the inventory.