negative ETA shrinkage

Dear all, I have found a negtive ETA shrinkage result in my model output. I did a simple simulation with 1-compartement model via iv bolus administration, and then refitted the simulated data with the same model and initial values. In the NONMEM output (of NONMEM 7), I got ETAshrink(%): -2.0123E-01 -2.3271E-01. From the definition of ETA shrinkage: 1-SD(eta*)/omega, eta* is the EBE estimated eta, there is no constraint preventing ETA shrinkage going below zero. Could somebody give me an interpretation of negtive ETA shrinkage? Thanks in advance! Maurice