Recent 'Preview' bug for transparent images in PDFs

I dont know if anyone else has encountered this but I suspect there may have been some recent change to Preview on MacOS

A PDF generated using DynaPDFMBS which contains a bitmap having a transparent background
Displays perfectly on screen
But when printed is a solid black blob

I already have a workaround (no transparency) , but I’m getting reports ‘all at once’ about code of mine that has not changed for years.

Remember something like this 10 years ago (or more), it was something to do with image format fr the bitmap and certain Epson printer drivers.

I recall we worked around it by drawing the picture into 32-Bit RGB SRGB colorspace image and then sending that to the print routine, which created the PDF.