Version: 1.9.5 (using KDE KDE 3.5.5)
Installed from: Gentoo Packages
KMail doesn't show kabc address book if the file containing it starts with a capital letter. I have three adress books: Mail.vcf, Handy.vcf and gesammelt.vcf. I just noticed that only the content of gesammelt.vcf was shown in the new mail form, so I tried to rename the others (to mail.vcf and handy.vcf) -- and voilà: the content of the others also appears after a KMail restart.
This issue is fixed in KDE4. Closing this report.