I think I'm seeing something similar, but it doesn't seem to happen all the time.
I sent a bunch of landers to Minmus. Each of them collected temp, pressure, and seismic data and transmitted it back to Kerbin.
If I try collecting the samples again the stock science dialog shows that I'll still get more science for it, but if I retransmit I get zero science.
Interestingly back at KSC in the research and development science archive tab all the experiments which have this problem show zero science data collected.