boinc version 7.6.33, 64-bit Linux 4.12.12
Only from Einstein@home project, I get lots (sometimes hundreds) of Event Log messages
"[unparsed_xml] FILE_INFO::parse(): unrecognized: report_on_rpc/"
on a project update / work request cycle. O.K., I know that I can ignore them by NOT SELECTING the "unparsed_xml" flag in the Diagnostic log flag dialog box, but if this is something that boinc does not support shouldn't someone tell the E@H administrators to fix it? In their <sched_reply_einstein....xml> file it seems that almost every <file_info> block contains a <report_on_rpc/> tag. It is NOT in the sched_reply...xml file of other projects I have running.
Was this a feature of (long) past boinc versions? I don't find any mention of it in the forum messages since 2014. Without the diagnostic flag enabled it is silently ignored and invisible to the boinc hosts. I'll be happy to advise the E@H staff if some boinc "authority" will confirm that this .xml tag is wrong.

It shows up in the checkin notes for 2011:

David  24 Apr 2011
    - client: simplify the semantics of sticky files:
        - All sticky files are reported on each scheduler RPC
        - If a scheduler reply says to delete a file, clear its sticky flag
        In particular:
        - remove the "send file list" tag in scheduler RPC replies
        - remove FILE_INFO::marked_for_delete
        - remove FILE_INFO::report_on_rpc
    - remove the request_file_list program

Einstein are using a fork from very old server code, because they didn't accept the changes to CreditNew made in 2010. I suggest you start a conversation with Bernd Machenschalk at Einstein to report your findings, and ask whether it would be safe to remove that tag from their code, remembering that people may still be using pre-2011 clients.

O.K., Richard,
I've posted to the E@H "Wish List" forum (thinking it not serious enough to qualify as Problem/Bug) and we'll see if there is any interest.
/Gene/