WhatsApp Web & Chrome?

Hi,

I'm using Chrome Portable very happily with one exception.
I can tell https://web.whatsapp.com/ to present a QR code that my iPhone WhatsApp app can scan, and it logs me in.
Everything then works fine as expected.

However, although the check-box "remember me on this computer" is checked, the next time I launch Chrome it has not remembered me.
The check-box / remembering me works fine on a regular non-portable Chrome.
And I don't think there are any differences between the cookie handling of either chrome user profiles etc.

Any thoughts?

TIA
Craig