Updating viewports - green tab blinking

[jasvars]

Hi there!

 

When I try to update some viewports in my sheet layer the loading bar show me the progress of the update of each viewport but mysteriously a green tab blinking in one of my classes in the classes window. 

 

Every time I click update the program start updating the viewport and randomly a class start blinking ( see screenshot ) 

Nothing bad happens after the program is done updating viewports but it looks weird for me since is the first time I see this happening to me.  

 

There is any reason Vectorworks is doing that?

 

thanks in advance