Bug in filled contours since version NCL 6.5.

[miub-weather]

Starting with NCL 6.5.0, a random-like bug in the filled contour plots being produced routinely at our institute (Institute of Geoscience- Department Meteorology of the University of Bonn) arose.

We plot GFS data obtained from the NCEP data server over a domain spanning from the West Atlantic to Eastern Europe, i.e. our plot domain crosses the prime meridian.
While we had never problems using NCL 6.3.0, the contours sometimes aren't filled correctly neither with NCL 6.5 nor with NCL 6.6.2.
More specifically, uniformly colored segments over several levels (which should have different fill colors) are drawn. These segments are likely to be confined by the prime meridian.
The problem seems to occur randomly since a small change in the plotting domain may yield a correct visualization and since the plotting process may succeed using slightly different data sets (i.e. another GFS data file).

The following plots show exemplary the issue:

This is the correct plot obtained with NCL 6.3.0.

The following two plots were created with NCL 6.5.0 and 6.6.2, respectively.

When the domain is slightly modified, NCL 6.5.0 (and NCL 6.6.2 as well) succeed in creating a correct plot.

The exemplary script and the data set (cropped data of GFS run 2019/01/23 00 UTC +087 forecast) can be accessed from:

link to script: https://uni-bonn.sciebo.de/s/I9dXjEAz8twDAtX
link to data : https://uni-bonn.sciebo.de/s/5lctA71qie3TSEp

Our system runs on Linux 4.12.14 (Opensuse 15.0) and NCL was installed by using the binary from NCAR.

Do you have any ideas how to fix this problem or is it related to deep bug in the NCL plotting routine?