If multiple X11 plot windows have been opened using the `set term x11 <n>` terminal option, then only the current plot window supports the entire range of mouse commands and hotkeys. The other windows will, however, continue to display mouse coordinates at the lower left.
For consistency with other screen terminals, X11 mouse support is turned on by default, wherever the standard input comes from. However, on some UNIX flavors, special input devices as /dev/null might not be `select-able`; using such devices with the mouse turned on will hang gnuplot. Please turn off mousing with `unset mouse` if you are in this situation.