[gmx-users] why do I have a "pressure scaling more than 1%" warning?

[nicolis at guideo.fr]

I run a MD on a small (18 atoms) drug in a 5x5x5 box with 4125 SPC waters.
I minimised with integrator=steep for 500 steps (yelding an energy of -218745)
and then launched an mdrun with integrator=md and dt=0.002.
After 188 steps I begin to see warnings:

Step 188  Warning: pressure scaling more than 1%, mu: 0.98803 0.98803 0.98803

that continue to appear every 2 to 5 steps.

I run with:

Tcoupl              =  berendsen
tc-grps             =  TLF      SOL
tau_t               =  0.1      0.1
ref_t               =  300      300
Pcoupl              =  berendsen
Pcoupltype          =  isotropic
tau_p               =  0.5
compressibility     =  4.5e-5
ref_p               =  1.0

I tried to begin with or without initial velocities but it makes no difference.
Is it a serious problem? And how to avoid it?

Thanks
Yiannis