If one assumes that isPopupTrigger() is dependent on the "feel" part of the
"look and feel" then this is a major bug. For example -

On Solaris (CDE/Motif) the right mouse button press causes the isPopupTrigger()
to return true. On Windows the right mouse button release causes the the isPopupTrigger() to return true. However if one runs the Swing application on
Windows in "CDE/Motif" look and feel isPopupTrigger() will behave like windows.
With Metal look and feel it gets wierder. It behaves like Motif on Solaris
and like Windows on Windows. There goes cross-platform feel aspect of Metal look and feel out of the window.

I think the problem comes from the fact that the isPopupTrigger() functionality
comes from the AWT and AWT is not supposed to know anything about a foreign
look and feel on a given platform.

It is not only isPopupTrigger() but a few other things too -

On Solaris(CDE/Motif) only left mouse click is supposed to select a object
from a list or tree (e.g. Try the CDE filemanager application). However
swing seems to ignore the distinction between right and left mouse button
clicks for selecting the objects. The objects are selected no matter which
mouse button was clicked. Try SwingSet Tree Panel or ListBox Panel