HTML is ON but keeps being disabled.

Hi,

when I make a post on my forum I style the < hr > tag with a html code.
I have set HTML to ON in my ACP and I click the checkbox : Disable HTML in this post so it is unchecked.
I hit Send so it updates my post but then it sets the checkbox back to checked.
http://webcoders.actieforum.com/t4-post-your-feedback-please-read
That's the link to the topic where I am trying to style my < hr > tag.
I have no css or javascript that changes this so I don't know why it keeps setting it to disable.

Please read this.
https://help.forumotion.com/t35636-enabling-html

Thank you Sanket, that worked.
Topic solved.