Found this conversation: Links to internal (Jive) content opening in new windows
However, it seems that the system adding target="_blank" shouldn't be performed for internal links.
In addition, when I inspected the HTML in a rich text widget I don't see the above was added, but I do see _jive_internal="true" was added to the href code.
I don't have ideas on what causes it, but we also tried to add this customization. In the end, we ran across too many strange cases where the behavior was unexpected/undesirable, so we removed it. The interesting thing is that while the external link opening in new windows annoyed a lot of people in the beginning, it seems to be one of those things that people just get used to.
FWIW, we have numerous web developers in our company, since web sites and digital marketing are part of our core business. These folks were extremely unhappy when we made this change. They insist that the current web standard is to open everything in the same window, unless the user explicitly says otherwise by right-clicking the link and choosing that option. It may not be what many of us are used to, but apparently this is the way the rest of the web is moving.