I have a problem inserting an image into a post from "add media", I had the same problem on 2.5.0, and upgraded to 2.5.1 hoping to resolve the issue. The image actually uploads, but the code is never inserted into the post. I get an error stating:
Error: Permission denied
I have updated Java on the PC just in case, I confirmed write ability to the server ( image is making it there ).
I get the same error if I select the image from the gallery, not just uploading an image.
If you have any ideas, I am willing to try them...