I’ve been adding posts from this blog to stumbleupon for a while.

But suddenly, I noticed that when I try to add a post to stumbleupon, I fill in all the required details, and when I hit the “Recommend this site” button, I then get a blank page.

At first, I thought there was something wrong, so I tried again.

Then I thought something was wrong with stumbleupon, so I decided to leave it until my next post a few days later.

But that also failed.

But I managed to find the cause: Stumbleupon will block you from submitting too many pages from the same domain.

So, self-promotion will only work about 11 or 12 pages, before you get blocked.

Stumbleupon will (rightly) not divulge the exact rules they use to block self-submitters.

But it would have been nice to get a warning message, rather than a blank web page!