Updating this publicly so I don't forget:
Turns out there's an issue with the current UI shaders where if your scene/canvas has too many elements with different alpha shaders on em, this bug happens (I think that's the cause, anyway). Unity's included GUI/Text Shader seems to render fine so that can be used for now, but I'm going to have to update the current shaders to work a bit more like unity's GUI/Text Shader.
So... until I rewrite the shaders, you can either use unity's included GUI/Text shader, reduce the amount of alpha elements/shaders in your UI, or don't use Unity UI with STM altogether. Thank you for your patience, everyone!