Strong Encryption lost

[halsnes]

I am using Office 2003 with the Office 2007 Compatibility Pack installed.
When I receive a Word file which is password protected (open) by Word 2007
(encrypted with AES 128), my Word 2003 shows that the encryption alogrithm
used is "Microsoft Enhanced RSA and EAS Cryptographic Provider (Prototype)",
which is according to Microsofts documentation.
When I encrypt a PowerPoint file however with PowerPoint 2007 and opens the
file on the computer running PowerPoint 2003, then the encryption setting
shows "Microsoft Base Cryptographic Provider 1.0", which is a much weaker
setting.
(When I repeat the process using Excel, the encryption setting shows "Office
97/2000 Compaitble", which is even more weaker).
All of the other ecnryption methods show in the drop down list
(Tools/Options/Security/Advanced).
Then I set the encryption level back to "Microsoft Enhanced RSA and EAS
Cryptographic Provider (Prototype)", save and close the PPTX file, then
reopens it again, using my PowerPoint 2003. The encryption level is back to
"Microsoft Base Cryptographic Provider 1.0".
Something seems to be very wrong here. (should I move this problem to
another discussion group?).