Paint.NET doesn't escape from the rule and load/save bitmaps as they were in 24bpp.
This plugin allow you to open and save file in 32-bit bitmap.
The only thing you must do is to rename it to *.bmpx (to avoid conflit with the existing PDN's BMP handler).
If you try to open non-BMP files, you should receive an error (rem: 24bpp bitmaps are loaded correcty too).
This plugin is perfectible and I'll publish updates if you find bugs/things to change.
Changelog [2.6 <== 1.xx] :
- Application optimised
- Fixed a problem of 1px translation on Windows
- Support now all bitmaps (and not only 32bpp)