Problems with form signing

[Miroslav Havram]

I have noticed that InfoPath allows to sign forms only if private key that
signing certificate points to is created with "Microsoft Enhanced
Cryptography Provider" or "Microsoft Strong Cryptographic Provider"
(PROV_RSA_FULL type of cryptographic provider), when private key that
signing certificate points to is created with "Microsoft Enhanced RSA and
AES Cryptographic Provider" (W2K3) or "Microsoft Enhanced RSA and AES
Cryptographic Provider (Prototype)" (WinXP), that is PROV_RSA_AES type of
cryptographic provider, InfoPath dont allow form to be signed.

Is this by design or... ?

Thanks,
Miroslav Havram