I knew someone smart who did that and it ended up being related to them having shift bound since they were a child to something they used differently than me, to change their inputs to Chinese pinyin.

In Microsoft's input method, shift will toggle you between ascii input and pinyin input while not switching you out of the pinyin input method environment.

I tend to use win+space, which instead toggles the input method you're using, as opposed to toggling how the pinyin input method interprets your input. But I had to learn about this secret special functionality of shift, because (some time ago; I don't know if it's still true) after switching your input method with world of warcraft running, the chat UI in the game would become nonresponsive.

After all, who ever heard of wanting to switch between different languages while using a chat interface?