When using a file upload type of assignment submission which allows for multiple submissions there is a blank submission created when the teacher set the students submission back to "Allow another attempt".

Student is shown two buttons -  "Add a new attempt based on previous submission"  and  "Add a new attempt".  The first of these will replace the blank entry but the second will create an additional new entry.

I can see why this would be useful for an online text submission (as you could simply edit the original text within the new submission) but this still creates an extra submission, which counts against the students allowed submission count and causes confusion for the teachers/students.

Steps to re-create:
Create a new File upload assignment which allows for 3 attempts
Log in as a student and submit a file
Grade this and set the "Allow another attempt" to yes (or set it to No and then later on the view all submissions page click edit -> allow another attempt
The result is a blank second attempt.
 
If the student resubmits using the button "Add a new attempt based on previous submission" then this replaces the blank second attempt.
If the student resubmits using the button "Add a new attempt" then this creates a third attempt which can be viewed.