SYN ACK scans to random ports

[silence_is_best () hushmail com]

Can someone explain the point of a SYN ACK scan to random high ports? 
I usually see a fair amount of these...at first I thought it was maybe
a block to an initiating SYN packet, but I don't see any evidence that
the SYN ACK isn't the first packet seen.  Danke. 

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