Self-Blocking SPIDs

My nightly DBCC CheckDB job is failing on the CRM Server, when it checks the MSCRM database. It fails because the SPID is blocking itself: and there's no point in trying to kill the SPID, because that just hangs. The self-blocking SPID also blocks everything else, rendering it almost impossible to stop the Scheduled Job via SSMS, as SQL Agent doesn't load. The self-blocking SPID also renders it impossible to stop SQL via SSMS or SQL Configuration Manager: the only way to stop SQL seems to be by killing the process in Task Manager (and that can't possibly be healthy).

There is, if one checks the sys.dm_os_waiting_tasks DMV, a lot of action going on in tempdb while this process is failing: the blocked resource is blocked on a LCK_M_IX wait_type, which is an intent exclusive lock. The memory involved in the process seems to be rather intensive (the memory used by SQL suddenly skyrockets). The executing SQL that is involved is really quite interesting: and not many people seem to have come across it based on a quick google about the place.

DECLARE @BlobEater VARBINARY(8000)
SELECT @BlobEater = CheckIndex (ROWSET_COLUMN_FACT_BLOB)
FROM { IRowset 0xE093909D00000000 }
GROUP BY ROWSET_COLUMN_FACT_KEY
>> WITH ORDER BY
ROWSET_COLUMN_FACT_KEY,
ROWSET_COLUMN_SLOT_ID,
ROWSET_COLUMN_COMBINED_ID,
ROWSET_COLUMN_FACT_BLOB
OPTION (ORDER GROUP)

So far, I have drawn a complete blank. However, I've decided that trying to increase the size of TempDB might be a sensible thing to do, simply because so much that is being blocked involves tempdb, and tempdb itself was about 8MB in size.