Brackets in markups stripped when using external writer

If I use an external writer to write and upload a post, the angled brackets <> get stripped from markup codes when opening it subsequently in the web-based editor. I can see the full markup codes for about half a second before the brackets get stripped.

This behaviour appears with WLW and w.bloggar, so it is not caused by the external writer.

Any idea what could cause this behaviour and what I could about it?

Thanks,
Michael