I came cross the same issue and updating "maxLinesConstraint" works for me:
http://splunk-base.splunk.com/answers/26392/show-most-relevant-lines-exceeds-500-limit
http://splunk-base.splunk.com/answers/559/how-do-you-tweak-splunk-to-display-an-event-that-is-more-than-500-lines-long
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