Changing brush settings is affecting all brushes (including tool presets)

HI folks, I'm not sure if this is an actual issue or if I'm missing something obvious, so I'm hoping somebody out there can resolve this for me.

The problem is this; I'm creating some custom, brushes and saving them as tool presets (.tpl files) to ensure they each retain their individual settings, textures, etc. However, if I alter the settings on any single brush, it applies the changes to ALL brushes, both the tool presets (.tpl) AND the standard brushes (.abr). This problem is happening every time I open Photoshop (and I have already reset the Photoshop preferences). Please tell me I'm missing something obvious!

Thanks in advance for any help!