Update 2 for Veeam Backup & Replication introduces new space update logic. When extent is assigned to a new task, service cache updates free space information with the real one and subtracts it with estimated sizes of all the tasks currently going to this extent.
You can switch to new logic by creating the following registry value:
Key: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication\
Value Name: SobrForceExtentSpaceUpdate
Value Type: DWORD
Value Data (Default): 0
A value data of 0 indicates disabled, and value data of 1 is enabled.