Empty PDF files in emails after update to 3.1.0

Hi everyone

After I have updated CodeIgniter from 3.0.6 to 3.1.0, because of the RSET and timeout fixes of the SMTP connections and suddenly have another problem at hand. When I attach a PDF file to an email. It arrives empty. Well, more precisely it arrives "size unknown" and I can't open it.

I use FPDF to create the PDF. But it works in 3.0.6, so I assume it has something to do with the inline attachment fix.

Does anyone have an idea?

All help is much appreciated.

Al