Scilab 5.5.2: several usability issues

Scilab 5.5.2 from Rapps has several usability issues that make it rather difficult to use:

• A strange flickering effect is observed all the time. Like if something were
  refreshed all the time.
• The Scilab console takes too long to start. And no cursor is shown. Hoewer
  you can enter a command and it works!
• You cannot access the menu item.

This happens both at r72051 and at r71014 (where Scilab has been previously reported to work in CORE-10977) so does not seem to be a regression.

My testing environment is Virtual Box 5.0.26 under Ubuntu 14.04