Duplicate invoice number in EBP

[Omkaram, Raju]

Hello All,
We came across in production system that the same EBP workflow event got
triggered twice within 6 seconds, both events have same invoice number from
the standard number range also the second event got processed before the
first one. The way the screen is set up that it would allow one time
creation of invoice by the user.
 
Have you come across of this symptom? What measures one needs to take to
prevent such behavior?
 
Thanks
Raju