Thanks for the replies folks. 

I went into paypal and did the refund of $7.15 and when I logged back into ebay ....next to the transaction was a message ...  Adjustment -$7.15

Seems it doesit  automatically .

Also I did have postage set at $7.15 with the cost per extra item set at $0.00. Its happened a few times now where it adds an extra $7.15 (or whatever the main postage cost was) all by itself. I normally check but this one slipped past me.

Anyway seems partials are done for you now ....

May have been like that for a while as this is the first partial I have done for yonks (since sales plummeted) .