VMware have released this Knowledge Base article.
If you have Change Block Tracking turned on (which is a sensible thing to do) and then you expand a virtual disk to be larger than 128GB, the data provided to the backup provider is wrong.
I haven't verified this with Data Protector, but I can't see any reason why DP wouldn't be affected in the same way as (say) Veeam, which uses the same mechanism.
Solution: turn off change block tracking, run a backup, and then turn change block tracking on again.
Greg Baker is an independent consultant who happens to do a lot of work on HP DataProtector. He is the author of the only published book on HP Data Protector (http://x.ifost.org.au/dp-book). He works with HP and HP partner companies to solve the hardest big-data problems (especially around backup). See more at IFOST's DataProtector pages at http://www.ifost.org.au/dataprotector