Looks like it is happening everywhere there is a dropdown.

Almost certainly the WP theme being a little overzealous with it;s CSS. Is it ClassiPress by any chance?
and we will need a link if we are to be able to advise…

Indeed it is ClassiPress! 

This is the forum page: http://swapsensation.com.au/swap-talk/

You will need to enter username: gate and password gate123 to enter.

Thank you very much!

Try the fix posted here:
https://simple-press.com/support-forum/sp5-general-topics/clear-instruction-on-how-to-upgrade-from-4-5-1/page-3/#p102724

Thank you for linking me up to the post.

I managed to get rid of the dubbel display dropdown boxes by adding this line:

#spMainContainer .selectBox-dropdown{display: none !important;}

after line 170 in my Clasipress style.css

yup just like we said.  nice job!

Well I would not have found this solution without you! Thanks heaps!