[Proj] Different results with +ellps and +datum

[Zarko Mocnik]

I noticed the following bahaviour of cs2cs:
 
with
proj -ld
I got:
__datum_id__ __ellipse___
__definition/comments______________________________
       WGS84 WGS84        towgs84=0,0,0
etc..
 
When I enter:
cs2cs  +datum=WGS84 +proj=longlat +to +ellps=bessel +proj=longlat
+towgs84=668,-205,442
15d29'1.2737 46d36'44.7813
I got:
15d29'18.941"E  46d36'46.661"N -21.034
 
But if I change command line to:
cs2cs  +ellps=WGS84 +proj=longlat +to +ellps=bessel +proj=longlat
+towgs84=668,-205,442
15d29'1.2737 46d36'44.7813
I got:
15d29'1.274"E   46d36'42.631"N 704.788
 
I would expect the same result (the first one) in both cases.
 
Is this I bug or a feature?
 
I use cs2cs Rel. 4.4.6, 3 March 2003 (I downloaded precompiled windows
version)
 




 
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