That example gives me "u as expected.
The full stop is not a dead key on my keyboard, but I am using a custom layout imitating the US Extended/ABC Extended layout from the Mac (
http://andrewdunning.ca/Mac-Keyboard-La ... r-Windows/) that has many things loaded onto AltGr (ụ is AltGr + x, u). If I switch to a layout without dead keys, the problem goes away, but of course that makes it rather difficult to type. Is that a known bug in AutoHotKey?