Odd Steam overlay behavior

[BlackGhost84]

I held off on updating Skyrim for the longest time in order to keep my mods stable. However, with the recent Steam updates, my game invariably got updated to the latest version. So after updating and troubleshooting everything, it runs normal again. The only annoying thing is when I press the Shift key to sprint, it brings up the Steam overlay. Not Shift + Tab, just Shift. This only happens once, unless I Alt + Tab out of the game and back in, in which case it will do it again. Is there anything I can do to disable this behavior? The only options in Steam that I can see are to turn the overlay off or change the key assignments. Personally, I don't use the overlay for anything other than the FPS counter and to be able to adjust the volume, since that's another thing I can no longer do in-game, but it would be nice to have. Has anyone else experienced this and is there a workaround? Thanks!