That's because the kerning tables in this font are woefully incomplete. The only pairs defined are "//", "Ke", "To", "We", "Ze", "Zo", "iz", "oz", "yp", "'r", and "'s".
Then again, Comic Sans from MS has no kerning at all.
The "fo" pair looks decent, but many others leave a lot to be desired. I don't have an explanation for the differences though. Maybe Libreoffice is using a different layout engine.
