To reproduce: Create a new document. In this document, create a new page style. Use "confetti.jpg" as the background image in the page style settings. Use 80% as the transparency indicator. This will be correctly applied to the page. Now save as .odt, .docx or export to .pdf; close Write and reload. The transparency of the background will be lost (ie. background image at full intensity). The exported PDF will also have the background at full intensity. There are many bugs related to lost transparency of background images in other places (eg. Calc), maybe they are related. Please have a look. Thank you!
*** This bug has been marked as a duplicate of bug 85757 ***