Actually,
I'm sorry. I believe I misunderstood null and thus delivered you a false explanation.
Steem doesn't get removed, SBD does and for a reason.
Your account didn't send to null. The promoting account's SBDs were automatically send to null, your wallet wasn't affected. You only got to see for how much worth of value you got promoted. That's how I understand it now.
When you make a post, there is the option to promote it with Steem Dollars. It will then show up in the “Promoted” tab. The order that it appears in the list depends on how much the post was promoted for. Posts with a higher promoted amount will be higher than posts with less.
Steem Dollars spent to promote a post are paid to the account @null, which nobody owns or controls. Once a user transfers SBD to @null, the Steem blockchain removes them from the currency supply. Details can be found in this official post.
ah ok!
It makes more sense now, I did try to promote a post when I first got the account. Thanks a lot for taking the time to dig this out @mielia - has taken a load off. Much appreciated. :D