Causes of CF (Control file) Enqueues on Index Creation?

We recently noticed, through Quest Performance Analysis, that a particular index creation statement on a newly populated table occasionally suffers from enqueue waits that extend the creation time from a few minutes to over an hour.    

  We used statspack to investigate further and found that at the time of index creation we get a spike in CF enqueue waits.    

  I have read Anjo Kolk's whitepaper "Description of Oracle7 Wait Events and Enqueues" http://www.akadia.com/download/documents/session_wait_events.pdf in which he identifies an imposing list of situations in which the CF enqueue is used.    

  The index is a locally partitioned single column uncompressed b-tree built in parallel degree 8 against a range partitioned heap table with 8 partitions. The table has just been loaded when this index is created and it's the first to be created post-load. Other subsequently-built indexes do not appear to have suffered from this problem. the index creation takes place in a new session that starts immediately after a previous session has populated the table, commited and gracefully exited. The issue occurs intermittently, not on every occasion that the table is loaded.    

  I don't have access to the statspack data we extracted at the moment ... I'll post it as soon as I do.    

  Does anyone have any quick thoughts about the relationship between creating an index and a control file lock? I'm really pushing the limits of my internals knowledge here -- OK, actually I have gone past it :(

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