Problem emptying trash after emailing attachments

Everytime that I email an attachment and then put that file in the trash and try to empty it I get an error that the trash can't be emptied because the file is in use. Twice today I had a file on my desktop I attached in an email and sent to somebody. Then I put it in the trash after it finished sending and tried to empty the trash and got this message. This was the first two times I've tried sending attachments since I just got this Macbook Pro the other day.

I noticed if I quit the Mac Mail program it will let me empty the trash. Does anybody know how to stop this from happening so I don't have to close the mail program everytime I want to empty the trash that has files in it I've emailed to somebody?

There is no way to stop this from happening, because what your computer is telling you is the truth.

When you're done sending, quit Mail. Now you can trash the files in question.

That is really annoying and a mistake within the OS that they need to resolve. The file is not in use so it's not the truth. Emailing an attachment does not justify the file being in use.