Coordinate system definition of EPSG:31259 contains false transformation parameters TOWGS84[601.705, 84.263, 485.227, 4.7354, -1.3145, -5.393, -2.3887]. Therefore the WMS renders pictures with a small offset (~1 meter) when transforming to EPSG:3857.
The correct parameters would be TOWGS84[577.326,90.129,463.919,5.137,1.474,5.297,2.4232] (http://spatialreference.org/ref/epsg/31259/ogcwkt/).
When defining a custom coordinate system with the correct transformation parameters, the offset disappers.
Probably an EPSG database is needed (see linked ticket) but it would take too much time to fit in spare time, and nobody has been available to sponsor the work so far.
Since I am from Austria I can confirm this. In the past I always had to use
my own WKT definitions to get the correct results.
Sorry for the late reply.
On Tue, Nov 6, 2018 at 5:44 PM Georg Ramler (JIRA) <
DI Christian Mueller MSc (GIS), MSc (IT-Security)
OSS Open Source Solutions GmbH