Floating (sticky, sticky) block on pure JS "twitches". How to fix?

Question

JavaScript

Good afternoon!
Tell me, a site on joomla, inserted an order module on the site, which crawls when scrolling, slides down, and stops along with the end of the page.
Did according to this instruction: shpargalkablog.ru/2013/09/scroll-block.html
I tried two options, but the result is the same. The block stops, but with further scrolling of the page, it starts to "twitch" and crawl onto the block, which is under the main text of the article. The behavior is the same on other browsers. Maybe a conflict with something from joomla? can you see with an experienced eye?

PS On the advice of one of the community members, I replaced pure JS with jQuery, but this did not solve the problem. Now the block does not twitch, but just falls into the basement, ignoring the "stop" element.
There is one nuance: when you change something in the script on the loaded page, it starts working correctly .. maybe it's the loading order?

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