Agent side checkout with private key from github fails (HP-Unix)

I'm experiencing a problem during agent side checkout on HP-UX 11.31

I've uploaded an ssh private key to the Team City server and I'm using this key on all of my agents for Github operation. It works fine on all platforms, but fails on HP-Unix with the following problem:

[Updating sources] Failed to perform checkout on agent: '/usr/local/bin/git -c credential.helper= fetch --progress origin +XXXXXXXXXXXX command failed. exit

code: 128 stderr: @ WARNING: UNPROTECTED PRIVATE KEY FILE! @

Permissions 0711 for '/home/lorban/BuildAgent/temp/buildTmp/key4455797951960803627' are too open.

It is recommended that your private key files are NOT accessible by others.

This private key will be ignored.

bad permissions: ignore key: /home/lorban/BuildAgent/temp/buildTmp/key4455797951960803627

Permission denied (publickey).

fatal: Could not read from remote repository.

According to the official documentation:

"During the build with agent-side checkout, the Git plugin downloads the key from the server to the agent. It temporarily saves the key on the agent's file system and removes it after git fetch/clone is completed."

Why does it save the key with execute flags (0711)? If I simply touch a file, it is created with the right flags (no +x).