Darn. I should have posted this three weeks ago.
My BD burner is OK. It’s just those crappy Chinese BD-Rs.
Tried a Verbatim 2x, recorded at 8x without problems.(Too bad Vetbatim media is expensive).I’ve also tried another one of those Chinese BD-Rs (made by Infosource), it recorded without problems but had like 600 read errors at the end of the disc (and that’s before I canceled the verification).
Also, ImgBurn worked better than Nero 8 when recording BD-Rs (and ImgBurn does not care about max write speed returned by blank media).

That’s all for now.