Advanced display filter: [^()]? in source and () or similar in target does not work

Question

I am trying to filter for segments, where the source does NOT contain any brackets, while target does contain at least one bracket. 
 I tried various combinations of [^()]? in source and [()] in target. But the result is:

I can only achieve results, when using [^(] in source and ( in target. But this should NOT work, as ( is not a valid regex. Same applies to ). 
 Am I doing something wrong or does ADF not cover this properly indeed?

Paul · Answer

Jerzy Czopik 
 Maybe try using a lookaround... like this for example: 
 ^((?!\().)*$ 
 \( 
 That filters this: 
 
 into this: 
 
 Which I think is what you're after?

Jerzy Czopik · Answer

Thanks Paul 
 I tried to try this, but must have inserted something wrong. This is exatly what I need.

Trados Studio > 6. Regex and XPath

Advanced display filter: [^()]? in source and () or similar in target does not work