ssh-agent: permanent loaded ssh-key storage

"OpenSSH for Windows" version
7.7.2.2

Server OperatingSystem
Irrelevant

Client OperatingSystem
Windows 10 Home (18362.418)

The problem
I am using private SSH-keys encrypted with a passphrase. When using any SSH-agent, that means I have to provide my passphrase to be able to load the key and use it. I've used pageant before and there you load the key and provide the passphrase. Whenever pageant gets terminated (by shutdown, rebooting, ...) the key is removed from memory, and I have to provide my passphrase again the next time I want to use it. Every time, hence the security advantage of having an encrypted SSH key.
With the windows openssh agent however, that's a different story. I have my agent set to automatically start with windows (I believe by running Set-Service ssh-agent -StartupType Automatic) just like I did with pageant. However, the windows openssh agent seems to permanently store my SSH key somewhere after loading it to the agent once (ssh-add), because when I run ssh-add l after a restart of my computer, they encrypted key which I loaded before the restart is automatically loaded again, without requiring my passphrase again. This completely voids the advantage of a passphrase-protected SSH key and to my opinion is a big security issue.

Proposed solution
Do not store my SSH key permanently when I load it into the agent, but only temporarily store it in the agent's memory. Or at least store it in it's passphrase-encrypted form and ask for my passphrase every time the key gets loaded.

Start by reproducing the behavior with the Windows ssh-agent service, ssh-add, and a system restart, checking whether the loaded key returns without its passphrase. Done means keys are held only for the agent session, or remain encrypted and require the passphrase again after restart; the 90-comment thread should be reviewed for prior conclusions.