Q&A: 500 error when answer consists of 20 000 symbols

Preconditions:
1. There should be Q&A created.
2. Q&A page should be opened.
3. User should have CREATE_TOPIC permission.

Steps:
1. Copy-paste 20 000 symbols text (attached file) into Answer the question field.
2. Press either Ctrl+Enter or Answer the question button.

AR: 500 error
ER: Draft is posted.

Watch
http://screencast.com/t/THKuq95jyj