Hi Mike,
I believe the defaults for Call History are causing this problem. Have a look;
show call history voice - Displays the call history table for voice calls.
To specify call detail record (CDR) storage time, use the dial-control-mib command, which has two sets of keyword and argument options. The max-size number option specifies the maximum size of the CDR event table. The valid range is from 0-500, and the default is 50. Setting the value to 0 disables the CDR feature.
The retain-timer number option specifies the length of time in minutes that entries will remain in the call history table. The valid range is from 0-2147483647 minutes, and the default is 15. Setting the value to 0 prevents any call history from being retained.
http://www.cisco.com/en/US/products/sw/voicesw/ps4625/products_configuration_guide_chapter09186a00804ad861.html
Call Activity Monitoring and Call History Logging
The Cisco Unified CME GUI provides call history table information so that a network administrator can monitor the call history information for unknown callers and use this information to disallow calling activities based on select calling patterns. The call history log should be configured to perform forensics and accounting and allow the administrator to track down fraudulent calling patterns. Configure the following commands to log call activity and call history:
dial-control-mib retain-timer 10080
dial-control-mib max-size 500
From this doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps4625/products_implementation_design_guide_chapter09186a00805f07a8.html#wp1077193
Hope this helps!
Rob
