Prior to upgrading to SP2, when strong private key protection functionality was set to high, you were prompted to enter your private key password every time that the private key is used to sign data, encrypt data, or to decrypt data.
Now, when you check the Remember my password box as you type your authentication, the cryptographic service provider caches your authentication, so you are only prompted to enter your private key password the first time that the private key is accessed.
NOTE: This behavior also occurs if you install the 821574 hotfix.
This change in functionality is documented in Microsoft Knowledge Base article 821574.
To workaround this behavior:
1. Open a CMD.EXE window.
2. Type the following command and press Enter:
REG ADD HKLM\Software\Microsoft\Cryptography /V PrivKeyCacheMaxItems /T REG_DWORD /D 0 /F