I agree with you that this bug does not seem to be a NeroLINUX problem, however are you sure it's a "kernel problem", or possibly a SuSE/mathf problem? I have been using 2.6 kernels for the last year and a half or so, mostly always with the latest and have never had this problem. I do not burn cd's very often, but every 2 months or so I burn a couple for my mother-in-law, and they have always been fine. They origionate from either CD, wav, ogg or mp3 (or sometimes a combination), and none of the formats have ever given a problem. This was up until recently using cdrecord via gtoaster.
At the moment I'm running 184.108.40.206 (the latest stable) vanilla kernel (up until this evening 2.6.11), with Nero 220.127.116.11, and still have no problems at all copying from cd to cd, or image to cd, or files to cd. I cannot test with > 10x speed though, as 10x is the fastest medium I have here, and my hardware probably would not support much faster (800MHz).
I just did 2 burns of an official CD, being a short CD (165MB's) to CD-RW from wav form like you did:
Both CD's were burned from WAV files created off the origional in this case. There is nothing wrong with them, and even more, they are detected correctly (cddb) from the burnt CD-RW. Data files have similiar ratios in terms of speed/time with no problems either.
I cannot reproduce the results you are getting (reversed speeds) either, which is strange, unless it only happens with > 10x burns (could you confirm by trying =< 10x)?
Just for the clarification ~ I helped Andreas Eckleder for about 2 years with beta-testing gnometoaster a few years ago. Although I'm not a programmer, I know gtoaster very well. Actually this is the reason I love NeroLINUX ..... and the fact that Nero provides it's own burning software under the hood is a bonus. If I can provide any extra info / testing just let me know mathf. I love to help.
At the moment I'm using a Asus DRW-1604P with Gentoo, as my old HP burner only supports 2x RW burning.