I contacted Nicholaas about this and basically the whole PayPal module is still in development and isn't really ready yet. Aside from the problem with it not submitting useful item names to PayPal, the whole reports section is incompatible with 2.3.0. and there are plenty of other bugs that I spent a couple of weeks trying to fix before I gave up. Apparently it's going to be ready soon - maybe the steaks will be raised now that 2.3.0 is a stable release...
What I did in the end was strip out all the fancy stuff and just added PayPal submission buttons to the Product.ss and ProductGroupItem.ss and Cart.ss templates. Instead of using static values in the button code for the submission of the item name and price I inserted SS variables:
<input type="hidden" name="item_name" value="$Title"/>
<input type="hidden" name="amount" value="$Price"/>
I've then removed the checkout and account pages so everything is done on through PayPal site. The only other thing that needs to be set up is the creation of 'successful' and 'cancel' pages that PayPal directs the user to when they exit.
It's rough and ready, but it works, and still allows the content manager to add new items without having to manually insert or edit any PayPal code.
Until we have a functioning PayPal module this is the only way to do it using 2.3.0 as far as I can see.
Hope that helps.