How can I prevent Ctrl+Shift from changing the text direction?
I haven't found how to disable the shortcut withing Windows, but if you're open to using AutoHotKey, there's a workaround:
Use AutoHotKey to map Right Shift to be Left Shift
No more RTL by mistake, and my Ctrl+Shift+← works without problem. I don't yet know of any reason why I need RShift, so I'm happy with this so far.
AutoHotKey mapping syntax is simple on this one:
RShift::LShift
Credit: Inspired by @gogowitsch in a comment on https://superuser.com/a/490244/93731