Custom Covers for News Periodicals Dissapear

[polamnus]

Hi, I'm new to the eReader world, just received a Paperwhite as a gift and really like it so far. Calibre is a really nice addition and I've been tinkering with it quite a bit.

I really like the news download feature. I've customized a few of my news feeds like Ars Technica, to incorporate a custom cover image by adding the line to the recipe:
cover_url = '...'

This works great, the news article in the Calibre window shows the custom graphic. When I transfer to my Kindle PW, a strange thing happens, and I suspect it's something the Kindle is doing, not necessarily Calibre.

The article shows up on the Kindle at first with the custom cover image at first. Shortly after that though, the cover automatically reverts to the generic Kindle cover image.

If I hold my finger on the item until the menu opens, there's the custom cover image. What's the Kindle doing to overrule the cover art? How can I stop or block this?

If it works for books, it has to work for news periodicals, right?

Many thanks for suggestions,
Pol