There's a bug on PIVx Wallet when running in Ubuntu 16.04.1 LTS, not critical but cosmetic and function bug.
When the icon is right clicked in the task bar, the menu is completely blank. If the wallet is closed, then one cannot retrieve the normal window wallet again because the taskbar icon is missing a menu.
unfortunately, this is one of the issues with Unity desktop and Ubuntu, and it is seemingly specific to just that combination (it is an issue with the Qt5 library supplied by Ubuntu and how Unity handles tray menus).
btw, this kind of issue report really should be made on github in the future. Don't rely on these forums to have your issue seen by someone on the dev team.