The same named parameter marker should not show repeatedly in the prompt window.
select :num from dual where 1 = :num or 2 = :num
shows 3 times 'num' in prompt window.
DbVisualizer 9.5.2 has just been released with a fix so that multiple identically named parameter markers are only prompted once.
Either upgrade using Help->Check for Update in DbVisualizer or download from our web site.
We have an open ticket to look into prompting only once for identical marker names. I will add your vote for it.