I don't think this situation will crop up too often but I bought >100 individually-listed items from the same seller (example auction ID 18898149).

The combined invoice came through OK (Invoice 66532) but when I clicked the integrated Paypal button only the first 99 items were displayed in Paypal so the total amount displayed was short of the actual amount due by a few £. I had to request a separate Paypal invoice for the remainder.

Also, the 'Return to Merchant' button in Paypal following a successful checkout returned a 'URL too large' message when attempting to switch back to eBid (the return address seemed to include each individual item number?). I have had this before when paying for multiple purchases (but in quantities of much less than 100).