Nope, you haven't changed anything, but you are correct it has happened only in the past few months, as eBay has introduced this feature .
When buyers make / accept an offer now, an immediate payment is made, this is introduced to stop the many non payments sellers were experiencing.
Whilst the idea is good ' on paper', it's not without it's failings, that is, you cannot select a payment method of your choice, no click and collect can be added ,or combining postage to name but a few.
To be fair sellers were not told of this either, and some / most, probably still do not know they have been opted into this. Only a seller can deselect this option.
All I can suggest is before you make accept an offer , is to message the seller to see if they are opted into this , can they opt out for you, so you can select a different payment method at eBay checkout.