I've had a similar problem before. To make it work, I added in an mp3 with a known ISRC code - then edited said code in SF9. After that, SF9 was happy with ISRC codes.
I'm using SF8 and did not see a place to add ISRC codes. Did I miss it?
Also remember I'm dealing with around 250 to 300 tracks each with it's own ISRC codes.
Plus in SF8 when I have it, create tracks from Regions, it give me a bunch of information that I do not want (the title of the track, the next title and the start and ending times). All I want is the title. So SF8 has not been that great for me.
Again for me it seems by the time I get everything in CDA, that has all the correct track names, the ISRC codes which I entered so from there, it they could standardize (or give me options) of what will go into the MP3 id area then that would be great.
For now it seems I have to burn the CD, then us a CD ripping software which import the CD text info and give me a half way decent mp3. However I'm have to burn the cd and then import that.