r u running TweakUI by any chance?
in
TweakUI under the
Mouse tab there r 2 options
Activation follows mouse (X-Mouse) and
Autoraise when activating
if you keep thes 2 enabled then widows will activate that window on which ur mouse cursor is placed (even if u dont click on it)
so if these features are enabled and while u r usin Word if d mouse accdiently moves some other place (say, the taskbar), then ur word document will no longer b highlighted
disable those and c if it worx