The Data Entry Statistics module (version 1.3) includes voided encounters and observations in the table of data entry statistics.
How to reproduce...
1.) Run the data entry stats for a period.
2.) Void an encounter.
3.) Run the data entry stats again for the same period.
The results of the data entry statistics will be the same.
If voiding something in OpenMRS is to be treated the same as deleting it, than this is a bug.