"Virtual Host Log": turning off "Use Server's Log" doesn't work

I'd like to log PHP errors separately for each Virtual Host, the same as access logs are.

VHost Template, Log tab settings:

User Server's Log: No
File Name: $VH_ROOT/logs/error_log
Log Level: NOTICE

But setting "Use Server's Log" to "No" has no effect: PHP errors are still logged to the main error log file.

Is this a bug?