When "Execute Command" filter is executed on incoming messages from an IMAP server the body of the message is not fed into the child program. The child program is receiving only message headers.

Reproducible: Always

Steps to Reproduce:
1. add simple script to filters to execute command everytime a new email message is downloaded
2. let that script just output to file everything it gets from stdin
3. check the file
Actual Results:  
You only get message headers without message body

Expected Results:  
The whole message headers and message body should be passed

After the message has been downloaded and you right-click and choose "Apply Filters" and select your filter with "execute command" with exact same script it works properly. It puts the whole email message (header+body) into the stdin of a child program.