Pets cannot be re-learned once sold?

I don't know if this is a bug that just effects me or if it effects everyone. I bought 3 Bombay cats from the crazy cat lady and learned them. I then caged all 3. If I buy another Bombay it won't let me learn it again. It says I "already have that pet". If I destroy or mail the caged pet to an alt, I still says I already have it. It will only let me re-learn the same 3 Bombays that I previously caged.

If I were to sell or destroy those 3 Bombays, then I could never have another Bombay in my spell book? Is this intended?