USERNAME always set to SYSTEM when running Bamboo as a service

Install Bamboo as a service using the guide as reported in https://confluence.atlassian.com/display/BAMBOO/Bamboo+installation+guide+for+Windows and the service will by default be run by the user SYSTEM. Now stop the service, change the log on user to someone else say user "JIRA" and restart the service. We will expect that the user running Bamboo should be JIRA but what happens is that the user still appears to be run by SYSTEM. This can be verified from the system info or using powershell commands from Bamboo builds:

Write-Host " My user name is $ENV:USERNAME and my computername is $ENV:COMPUTERNAME"

See screenshots for an illustration.