Font file is being held by system process

Question

In my environment, a TTF file(font file) is being held by system.exe process.
I can't understand why it's happening.
I've tried to unregister(uninstall) the font and still the system process is holding it.
My problem is when when i update the package with th ttf file, it requires system restart since the file is replaced while being held.
Does anyone have any suggestion why it is being used by system process and what can be done?
Thanks

Answer 1

This behaviour was introduced with a security update released in August 2014 (refer to security bulletin MS14-045 for details) and applies to any font file that is not installed in the default fonts directory.

Although the KB article for MS14-045 lists this as a "known issue" it is now documented as the expected behaviour. See Font Installation and Deletion in MSDN:

A font installed from a location other than the %windir%\fonts folder cannot be modified when loaded in any active session, including session 0. [...]

Permanent fonts remain installed after reboot and are loaded by all created sessions.

This means that if it is not acceptable to have to reboot the machine when upgrading the font, the font file must be installed in the default fonts directory. (I believe this has always been the recommended practice in any case.)