[Proj] UTM ED50 to ETRS89 datum shift problem

[karel cech]

Hi list,
I have a problem with changing datum with cs2cs using 7 parameter
shift from ED50/UTM30 to ETRS89. The result differs a lot from
transformation results made by Carthographic Institute of Valencia
(they work with ESRI and ERMapper)
My test point has following coordinates (ED50/UTM30, EPSG:23030)
720931.9
4376574.85
What I would like to obtain is aproximatly this (ETRS89, EPSG:25830):
720821.51
4376365.31
However, cs2cs gives me
720748.93
4376357.47

The 7 parameters are defined by spanish institutions.

The debug output from cs2cs (proj 4.4.9.):

cs2cs -v +proj=utm +zone=30 +ellps=intl
+towgs84=-131.0320,-100.2510,-163.3540,1.2438,0.0195,1.1436,9.3900
+units=m +to +proj=utm +ellps=GRS80 +zone=30 +units=m -r <<EOF
> 720931.9
> 4376574.85
> EOF
pj_open_lib(proj_def.dat): call
fopen(/usr/local/proj4/share/proj/proj_def.dat) - succeeded
pj_open_lib(proj_def.dat): call
fopen(/usr/local/proj4/share/proj/proj_def.dat) - succeeded
# ---- From Coordinate System ----
#Universal Transverse Mercator (UTM)
#       Cyl, Sph
#       zone= south
# +proj=utm +zone=30 +ellps=intl
# +towgs84=-131.0320,-100.2510,-163.3540,1.2438,0.0195,1.1436,9.3900
# +units=m
# ---- To Coordinate System ----
#Universal Transverse Mercator (UTM)
#       Cyl, Sph
#       zone= south
# +proj=utm +ellps=GRS80 +zone=30 +units=m
-67.69  720748.93 175.19
-102.91 4376357.47 82.19

I am sure have missed something or misunderstood proj. For, example,
according to manual, using 7parameters shift provides the option
+towgs84, but, I don't output to wgs84.. Do you use +towgs84 in similar tasks?

Thank's in advance for any ideas,
Karel