Transformed attachment filenames

I am using the IMAP-POP3 email module. On certain email attachments (only some pdf's) the attached filenames are being changed as the emails are read from the external mail server. The string '=-iso-8859-1-Q-' is added to the start of the filename  and '-=' is added to the file extension. as an example      170214_B_KFI_=A3650k_fixed.pdf is transformed to      =-iso-8859-1-Q-170214_B_KFI_=A3650k_fixed.pdf-= which means that the file cant ve viewed.

Any ideas.

Thanks, Ray