As a result of an investigation done by meta-inf-kft about how the Email this issue Plugin uses Velocity Templates in Jira, it was discovered that the objects from class DefaultVelocityManager might be causing memory leaks.
DefaultVelocityManager is currently part of our Jira API that can be used by Plugin vendors.

Turns out that Jira uses another object to handle Velocity templates: JiraVelocityManager which is safer to use, and is confirmed by Atlassian development team to be the recommended class to be used for working with Velocity templates.

Thus, we need to make the objects from the class DefaultVelocityManager marked as deprecated so that our plugin vendors know that it is not supposed to be used any more.