Agilent 8860 retention time shift on only one column, for only one injection

We have been encountering this problem since shortly after installation, and while it is not a large problem and so haven't made too much fuss over it, it is still odd and can be quite inconvenient. We run our GC with 2 columns, and what is happening is that while going through the data analysis of one of my runs I will come upon a sample where I notice the peaks have shifted away from their retention times, for example in one of my last runs the peaks showed up about 0.05 min later than they should have, but only on one column/signal. So for example this time it happened on signal 1, but I have had it happen on signal 2 before. Every other shot in the run is perfectly fine, the data on the other column is fine and everything is normal and within the retention time window on that one. Is there any reason for this happening or something that can be done about it? I can't understand why it would shift on only one column and only one shot, I've never encountered this with any of our other GCs.   

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