Description:
When a inserted a image file and applied 50% transparency has no effect. But if a save a file with .docx format and open it on microsoft word the transparency effect work foor headed only.

Steps to Reproduce:
1.insert a image file on the header or in the document body.
2.click on it, and open "properties" menu by right button of the mouse
3.Select transparency tab options
4.select transparency radio menu and put 50% value or other value.

Actual Results:
The libreoffice writer don't render the transparent effect. But in my environment has strange behavior for:

1) image file insert on header -> Libreoffice writer don't render it but save it using .docx format and open on microsoft office, the transparency effect work appropriately.

2) image insert on document body -> the transparency effect didn't work in the libreoffice writer and on the microsoft word the file (.docx) effect didn't work too.

obs: I nstalled by snap package (stable version)
https://snapcraft.io/search?category=&q=libreoffice.

Expected Results:
the transparency effect works in the libreoffice write and Microsoft's archive (.docx), saved by libreoffice writer, works appropriates on the microsoft office.


Reproducible: Always


User Profile Reset: No


OpenGL enabled: Yes

Additional Info:
Extended renderer info (GLX_MESA_query_renderer):
    Vendor: Intel Open Source Technology Center (0x8086)
    Device: Mesa DRI Intel(R) HD Graphics 5500 (Broadwell GT2)  (0x1616)
    Version: 18.2.2
    Accelerated: yes
    Video memory: 3072MB