Losing part of article class on change

Hi,
When moving from the first page to another (either manually or automatically), the article is losing part of it’s CSS class.

Example, in a 2 post loop, in a page, as a SiteOrigin widget:
– loading the page, i get this:
<article id=”post-2398″ class=”post-2398 post type-post status-publish format-standard hentry category-uncategorized”>
– moving to the next page:
<article id=”post-1996″ class=”post-1996 type-post status-publish format-standard hentry category-uncategorized”>
– moving back to the first page:
<article id=”post-2398″ class=”post-2398 type-post status-publish format-standard hentry category-uncategorized”>

The post class gets lost somehow. Any idea why this should happen?
Thanks.

PS: one of the most customizable and useful plugins I have seen. Thanks for this.