Post creation: After validation error the error persists even if it's fixed

Steps:

1. Create Discussion
2. Leave 1 symbol in the response and submit the form -> you'll get a validation error
3. Type some more letters to comply with the validation constraints
4. Refresh the page

AR: Page is refreshed and the newly entered text is present, but validation error is still present.
ER: Page is refreshed, the newly entered text is present and the validation error is absent.

Technical Details:

• Because we use Spring Flash Attributes to implement POST/Redirect/GET pattern the validation error persists in the user session even after the redirects. We need to research possible solutions as well as alternatives to POST/Redirect/GET to come up with something that perfectly fits expected results. As a result we should have both the fix and the research results with the justification.
• Also note, that in most of the cases we don't use POST/Redirect/GET pattern and rely on browser showing the warning. This solution also should be considered.
• Please check out Questions-n-Answers plugin as it doesn't use POST/Redirect/GET pattern