Add to Basket error

[Guest gwawr]

I'm experiencing an issue with the 'add to basket' process :

I'm running a store with SSL. When a user makes their first visit to the site (using the standard HTTP request), the session is initiated with a value of NULL for the basket.

When a user views a product page, they are in standard HTTP, and click the 'Add to Basket' button, the add process takes place in combination with the switch to SSL mode.

When the user then views their basket, it's empty. The Basket value (serialized array) is not not null.

If the user goes back, or visits another product, and then adds a product again, it now works.

So in summation, the first time a user attempts to add a product to their basket it fails, but works from thereon in.

I've not been able to fix this but have worked around it by switching the site to SSL more one step earlier in the process, when users view a product page.

I'm running a heavily hacked and edited version of 3.09 - but has anyone else experienced similar with a base install of 3.09?

Edit : It's also worth noting that although I've hacked at the layouts and view products pages, I've not altered any of the session initiation code, or the ssl switching code.

Thanks