Why changes in UiLabels.xml require a restart?

[Ejaz Ahmed]

I was expecting changes in UiLabel.xml file (found in particular application) 
should not require OFBiz restart. But it is not the case. I mad an experimental 
change in product component and refreshed OFBiz page. Changes were not updated. 
Then I cleared browser caches, no changes. I had to restart OFBiz application 
for this change to affect. Why a restart is required? Does ofbiz loads UI 
Labels at startup only? 

Regards:

Ejaz Ahmed