It's a pretty simple thing. There's a character in Y Gwrachod ( Roald Dahl) called Mrs Spring. But the next time she is mentioned, she gets called Mrs Sbring !
After that she goes back to being called Mrs Spring again. Twice.
Now as far as I know, the p-b soft mutation doesn't extend its claws inside a word ... plus, also as far as I know, proper names are "resistant" to SM anyway. So what the hell is going on? Or ... is it just a misprint which just, by an incredible coincidence, happens to mimic an SM ?
Come on somebody, tell me what that's all about.
Or not, as the case may be.
Meanwhile, Y Ffug will regale us with "Coffi Du" .....