Every version later than 0.6.16 seems to have some problem with the java-script refreshing the wall display view in Opera. The screen blinks or becomes blank for a fraction of a second at every refresh. The more jobs in the view, the worse it gets. In version 0.6.16 everything works fine even with many jobs in the same view.

PS. Changing to a different browser is not really an option as Opera is the only one displaying the bars in flat colors instead of the shaded ones (that seem to be default and not configurable in the latest versions of the plugin)