[MC-260731] Worlds use custom block and entity tags despite having no datapacks installed at all

I unfortunately have no idea how to replicate this, all I can say that might be useful is that I tend to create a lot of new worlds because I don't use the /reload function whenever I change something in my datapack, I instead create a new world to test things.

But now I was messing around and I found out that despite having no datapacks enabled at all, block and entity tags from a custom datapack were present.

The following video perfectly demonstrates what is happening, watch for yourself on the F3 screen at the side for the block tags: (I wasn't showcasing entity tags in the video but I tried it off-camera and they also work the same way)

Link to YT video: (sorry, I don't know how to embed here)

https://www.youtube.com/watch?v=Z9fySJ8XUOU

If it helps, here is the #time:air_valid json:
^{
^"values":[
^{"minecraft:air",}
^{"minecraft:void_air",}
^{"minecraft:cave_air",}
^{"minecraft:water",}
^{"minecraft:lava",}
^{"minecraft:grass",}
^{"#minecraft:flowers",}
^{"minecraft:fern",}
^{"minecraft:fire",}
^{"minecraft:tall_grass",}
^{"minecraft:large_fern",}
^{"minecraft:vine",}
^{"minecraft:twisting_vines",}
^{"minecraft:twisting_vines_plant",}
^{"minecraft:weeping_vines",}
^{"minecraft:weeping_vines_plant",}
^{"#minecraft:crops",}
^{"#minecraft:saplings",}
^{"#minecraft:signs",}
^{"#minecraft:buttons",}
^{"minecraft:attached_melon_stem",}
^{"minecraft:attached_pumpkin_stem",}
^{"minecraft:nether_wart",}
^{"minecraft:sweet_berry_bush",}
^{"minecraft:cocoa",}
^{"minecraft:sugar_cane",}
^{"minecraft:dead_bush",}
^{"minecraft:seagrass",}
^{"minecraft:tall_seagrass",}
^{"minecraft:redstone_wire",}
^{"minecraft:rail",}
^{"minecraft:powered_rail",}
^{"minecraft:activator_rail",}
^{"minecraft:detector_rail",}
^{"minecraft:torch",}
^{"minecraft:soul_torch",}
^{"minecraft:redstone_torch",}
^{"minecraft:glow_lichen",}
^{"minecraft:snow",}
^{"minecraft:tripwire",}
^{"minecraft:mangrove_propagule",}
^{"minecraft:frogspawn",}
^{"minecraft:sculk_vein"}
^]
^}