CDC and sys.dm_db_task_space_usage.internal_object_alloc_page_count

Gurus -

I have CDC setup (2008 R2) and the job is set to run continuous. The job calls the cdc scan procedure with default parameters
maxtran = 500
maxscans = 10
continuous = 5
pollinginterval = 5

Attached are the properties of the sys.dm_db_file_space_usage
database_idfile_idunallocated_extent_page_countversion_store_reserved_page_countuser_object_reserved_page_countinternal_object_reserved_page_countmixed_extent_page_count
215062800592 4288840
235061920576 4488744
245064000616 4232752
255064720512 4288728

sys.dm_db_task_space_usage for session 54 (cdc job session)

session_idrequest_idexec_context_iddatabase_iduser_objects_alloc_page_countuser_objects_dealloc_page_countinternal_objects_alloc_page_countinternal_objects_dealloc_page_count
5400292482924814341360

sys.dm_db_session_space_usage for session 54 (cdc job session)

session_iddatabase_iduser_objects_alloc_page_countuser_objects_dealloc_page_countinternal_objects_alloc_page_countinternal_objects_dealloc_page_count
542000 0

In "sys.dm_db_task_space_usage" the "internal_object_alloc_page_count" column increases gradually and the "internal_object_dealloc_page_count" doesnot change. 

This intern means that the session uses space in the tempdb that gradually increases. It used to be in MB's now have moved to GB's.
But this doesnot add up to the output from sys.dm_db_file_space_usage (429840 in dm_db_task_space_usage is much higher that the sum of the four rows for internal_object_reserved_page_count column in sys.dm_db_file_space_usage) -Yes I have 4 tempdb data files

Questions:-
1) Why is the dealloc not happening for the CDC job - (It deallocates for other processes that are continuously running like replication jobs in our system)
2) Why is the counts not making sense

Appreciate help understand!

Thanks