WLM : Emails displaced to file are erased !

I'm a new member, then hello everybody.
I'm trying to help a friend who has the following problem with WLM 2011 :
when she moves emails (any) from the inbox to a dedicated file (say, "archive") to organize its mails, their contents disappear and are replaced by copies of the first email which was once displaced into this file. Then, all emails in a file become copies of the first, and contents are definitively lost. How to fix that ? it works fine on my own WLM. Re-installing WLM (any risk?)
Thanks for the help.
My friend's config :
Win7 32 bits, WLM 2011, standard installation, one user (admin), no other problem.

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