Some Audio CDs K3b consistently refuses to copy, no idea why (large number of tracks in all cases, though): Image files are written, all burning media are OK...
Some kind of fix: Start the copy as usual, but don't remove the image files. K3b aborts as mentioned above.
In the temp directory shown in the burning dialog you will find all extracted audio files. Burn a new Audio CD, then remove the temp files.
PS: The hard limit set by the CD standards is 99 tracks - I had about 40 each. K3b is weird.
PPS: If you are totally fed up with K3b, try console copying.