There are two methods that can be used to save the contents of the window when it's not currently displayed: backing store and backing pixmap. Some X-servers seem to support only backing store (eg. VAXstations) and some only backing pixmap (eg. some X-terminals, including EWS).
In order to force gv to use one method or the other, use the
State | Setup Options ... menu and toggle the "Backing Pixmap" button.
When selected/highlighted (normally the default), gv will use backing
pixmap; otherwise it will use backing store. Select "Apply" to use a new
setting and "Save" to make it the new default.