Elimination of widows/orphans in books converted to KFX is working for me.
Assuming that wasn't the end of a chapter, your image from the Oasis does look like the default widow/orphan handling for KFX is being performed. If so then your attempt to eliminate it using the extra CSS method is not working. Make sure that you have entered the extra CSS correctly.
If you examine a conversion log to KFX you should see the following listed under "Conversion options changed from defaults":
Code:
extra_css: 'body {orphans: 1 !important; widows: 1 !important}'
If that is the case and the book still isn't working then you could try doing the same conversion for a public domain book and posting the resulting KFX file here so that I can examine it.