Lead Insert Trigger Fires Both Insert and Update Events in Lightning UI but Only Insert in Classic or Apex

Hi Everyone, 

I am facing an issue with a Lead trigger in Salesforce. 

When I create a new Lead from the Lightning Experience UI, both the before/after insert and before/after update trigger events are getting executed during the same transaction.

However, when I create the same Lead from Salesforce Classic or apex, only the insert

trigger events are executed, which is the behavior I expect. 

Has anyone experienced this behavior before? Is there any standard Lightning behavior that causes an immediate update after record creation? 

Please help me out.  

Thanks