Feed burner subscribe by email

I found a bug in the "Pixel" theme.

You can't subscribe to the Feed with email if you put full link to feed burner in the theme options.

And if you put only your username then you can't use the "RSS" button.

Example:

if I put full link to my feed burner e.g.
http://feeds.feedburner.com/Apower

Then subscribe with mail does not work

If I only put my user name
Apower

Then subscribe by mail is working but not the "RSS" button.

Best regards,

Apower