Functions don't accept command source parameters, causing issues on servers

Possibly Spigot-related, but probably also Minecraft-related. Functions will not accept source indicators at the start of commands (for instance, minecraft:tp), meaning that there is no known way to circumvent plugin interference to the best of my knowledge. When I load my functions files into the game with the above command, it registers as an error on start-up and won't throw the command when needed. The game won't simply accept the tp command either- entering an identical command into a repeating command block will work (with minecraft: prefix), but using either tp or minecraft:tp in a functions file will not.
As far as I can tell, when you get in the game, it considers tp to originate from whatever conflicting plugin takes priority over the default.