Laptop, Windows 7, Chrome, all up to date everything.
I want to tag users in posts here. I type @ sign and start typing their username....as I would if @mentioning someonw on twitter.
So...
wittierInteresting.. That happened to me on a laptop with the same specs as the one you mentioned. However, if I used my Windows 8.1 laptop, I don't get the same results. Possibly a bug.