The update-PDF butto currently does nothin, Neither on Windows, nor on Linux: http://bugzilla.lyx.org/show_bug.cgi?id=3573
On Windows you can just press in any case the PDF button and the PDF is already opened, it will be updated, if not the PDF is created and opened in a viewer. When this is the same on Linux we can get rid of the Update button, if not we should fix this for LyX 1.5.0 as I got some complaints about this the last days from beta-testers.
regards Uwe
