I have seen the same problem in one of my installations, but I have a test installation that does not have the problem. The only difference I know of is that I changed my nickname for admin on the system with the problem while on the test system I created a separate user for myself... besides the different base system name differences. I'll diff the two installations and see if I can notice anything of interest. Even with the error messages my posts are deleted.
I believe I tried to delete a post as admin on my test system, but I will double check that.