What's the Name of That Book??? discussion

I read this book about 20 years ago. All I can remember is that it takes place on a planet run by witches. Three friends are journeying by ship, when they are put in prison and a cat materialises ad dematerialises in their cell. The book was quite humorous and might be part of a series.

Maybe A Sudden Wild Magic

or one of the Witch World series by Andre Norton?

Thanks, but the book isn't by either Andre Norton or Diana Wynne Jones as I have all their books. It's more like a Terry Pratchett, or Robert Rankin.

Maybe The Witches of Karres?

The Cat who Walks through Walls, RA Heinlein

The Cat Who Walks Through Walls for stormhawk's suggestion

All good suggestions but it's not any of them - I've reread them all before posting my original question. I'm pretty sure it's not a well-known author ( or wasn't 20 years ago) as I reread those regularly. I'll have to go through my collection again for the books that are hiding behind the front row! One of my difficulties is that I may have loaned it to someone, as I often do with books I've enjoyed, so it's possible it's no longer on my shelves.