This applies to Screen Widgets and context and global context are alive while a screen is being built.
This ofbiz developer put it well:
Each piece of a screen has its own context, and there is also a global context
available to all scopes. This is only available during the screen
rendering process. Once the screen is rendered, there is no more
context.
In general the only way to keep variables across
multiple requests is to use the session.
