Kmail 2.8.: 'Find messages' won't work

(Using KMail 2.8.2 in a fully-updated 64-bit Mageia-2 Beta3)
Overall I'm very pleased with KMail, especially how well it maps Local Folders onto an existing maildir email set (/kmail/mail).
But I've just struck an unexpected problem with Find Messages:
When I try to Find Messages whose e.g. headers (or whole message) contain a certain string, the Find fails:
""Cannot get search result. Unknown error. Only resources can modify remote identifiers."
What on earth is that all about?! Surely a Find is not modifying anything?
Unless someone can provide a solution soon I shall be reporting this as a bug...
HELP!
Overall I'm very pleased with KMail, especially how well it maps Local Folders onto an existing maildir email set (/kmail/mail).
But I've just struck an unexpected problem with Find Messages:
When I try to Find Messages whose e.g. headers (or whole message) contain a certain string, the Find fails:
""Cannot get search result. Unknown error. Only resources can modify remote identifiers."

What on earth is that all about?! Surely a Find is not modifying anything?
Unless someone can provide a solution soon I shall be reporting this as a bug...
HELP!