Splunk add-on for Blue Coat ProxySG: Why are the logs arriving fragmented on the Splunk Heavy Forwarder?

Hi splunkers! I just add a new BlueCoat box as my new proxies. After configured it just like my actual one, the logs arrived on the Heavy Forwarder ethernet interface, but they arrived fragmented on multiple small frames, With approx 1600 Users logged on this new proxy, I'm quite sure that the logs received are not complete. My SGOS version is 6.7.3.1 Does anybody encounter this kind of problem? Thanks. Olivier.