librecalc picture in background not saved

In several of my worksheets I have included pictures in the background. When I save the spreadsheet and re-open it, all my pictures are in the foreground again.
What could be the issue here ?

… and you are saving your documents in which format (.ods or any other) on which operating system using which LibreOffice version?

My 5ct guess: You don't use `.ods` and may be you want to file a bug report on `xlsx/xls` export filters here

Saving in XLSX format, using LibreOffice 7.0.3 on Windows 10
btw saving in ODS format, does NOT produce this bug

Saving in XLSX format,

Don’t use alien formats, if there is no real use case for that (there are - and always will be - compatibility issues),