I have Sparrow configured for my personal gmail account, and Mail.app for working. However, every time I open Sparrow, it will set itself as the default .eml file reader, although I didn't config the Sparrow doing so (as in the following picture). I like to use the Mail.app as the default .eml file reader, so every time after I use Sparrow, I have manually re-config the .eml file reader to Mail.app.
Is it a Sparrow's bug?
