My current setup is one panel along the top of the screen.  If a window occupies the entire remaining height (when it's created), it's not possible to move or resize it vertically.

For example, Epiphany was last used here in a tall window, that went from just below the panel to the bottom of the screen.  When I launch Epiph, it reappears in that size.  It's not maximized.  But I can't move it up or down -- just left and right.  I can't resize it vertically, either -- only horizontally.

The trick I have to use is maximize/unmaximize.  Then it acts like a normal window again.

This is Metacity 2.18.3 in Debian.  I don't remember this happening before, but I don't know what version started this behavior.