There must be some slight difference in the way things are set up regarding this font between your Macbook and your iMac, but I don't know what that might be.
I gather you are planning on this font being embedded in your book, since it is not present in iOS. Have you exported to .ibooks format and tested it on an iPad to see if that works as you expect?
Yes its been working fine in all preview tests on my iPad and others in the company.
Plus my Macbook is a carbon copy of my iMac (i use CCC to clone the iMac HD)
Someone suggested that the two ways to change fonts in IBA causes some differences, apparently the top left dropdown menu when selecting fonts only show whats available for embeding and the drawer you get by clicking the 'A' in the top right shows all the fonts on your system.
Still cant figure it out!!