Why do PNG images render badly in LibreOffice

PNG images looked great in earlier versions, pretty much identical to the rendering anywhere else. But now they look blocky and almost unreadable. I’d think this was a bug, but would something so obvious get through testing? Hoping this is not a deliberate change, because this version is almost unusable (for me).
Version, EN-GB, Writer, Mac OS 10.10.2 English (UK)

The bug report is linked from Why hasn't the awful PNG rendering been fixed (for 3 years!)?.

I made a test on an XP machine using v4.3.6 (normal) and 4.4.0 (portable) but could not see any difference.

Is it a Mac problem?

When you look at these png-images with a normal viewer, do they display the same size as in your Writer document?

This problem doesn’t occur in earlier versions - only and onward. Documents created with earlier versions look fine in the original version, but look terrible if opened in I’ve also tried in and the problem persists. The documents also look perfect in OpenOffice or when exported to PDF. Only the latest versions of LibreOffice are rendering the PNG images badly. I’ve been using OpenOffice/LibreOffice for years now, and this is a very marked change.