--- a/schema/isrs_functions.sql	Tue Jan 15 18:09:10 2019 +0100
+++ b/schema/isrs_functions.sql	Tue Jan 15 19:46:41 2019 +0100
@@ -65,12 +65,19 @@
                         FROM from_point, to_point) AS points
                 WHERE ST_Covers(ST_Buffer(lines.line, 0.0001), points.pts)),
         axis_substring AS (
-            -- Use linear referencing to clip axis between distance marks
-            SELECT ST_LineSubstring(
+            -- Use linear referencing to clip axis between distance marks.
+            -- Simplification is used to work-around the problem, that
+            -- ST_LineSubstring might generate very small line segments at an
+            -- end of the resulting linestring, that significantly differ from
+            -- the direction of the input linestring due to finite precision
+            -- of the calculation. The generated small segment of the
+            -- resulting line leads to unexpected results of the buffer with
+            -- endcap=flat in the CTE below.
+            SELECT ST_SimplifyPreserveTopology(ST_LineSubstring(
                     axis_segment.line,
                     ST_LineLocatePoint(axis_segment.line, from_point.geom),
                     ST_LineLocatePoint(axis_segment.line, to_point.geom)
-                ) AS line
+                ), 0.0001) AS line
             FROM axis_segment, from_point, to_point),
         range_area AS (
             -- Create a buffer around the clipped axis, as large as it could