Prefill syringes & backflow

[Hallene E Utter]

Has anyone else had problems with the prefills "backing up"?  What I mean is after you remove the cap and push the fluid up to the tip, if you take your thumb off the plunger for an instant, the plunger and fluid slip back a bit.  This is not so significant before you flush in terms of a significant amount of air,esp in adults,  but if you are using a neutral displacement valve cap and you release your thumb from the plunger before you unscrew the last syringe (which would be normal in my opinion), it allows for blood to back up in the tip of the line.  Even with a positive displacement cap, I am not sure the over flow with unscrewing is adequate to flush this backflow back out of the tip thoroughly.  Particularly important if only using saline flushes.  Anyone else seen this phenomena?  Even clamping before you unscrew, unless you keep your thumb and hencefore pressure on the plunger, would not prevent this "plunger slippage".  Any comments?  I had the ICU nurses point this out to me and they were sure right.  The fluid slips right back into the syringe after you push it up to get ready.