Unable to change Large Letter 1KG default option in Simple Delivery

Earlier today I was able to list two football programmes and select Small Letter up to 100gm as posting option to override the default Large Letter 1kg. This evening only the Large Letter option is available with no option to change this. For info, i am creating an auction listing starting at £0.75 that only needs a small letter postage charge without tracking.

is this a fault in the listing process.