Problem: In ArcMap, short hash line symbols do not display on some line segments
In ArcMap, short hash line symbols sometimes do not display in ArcMap on some line segments.
This is a known caveat for on screen display of very short hash line symbols due to the performance enhancements implemented at ArcGIS Desktop 9.3.
Solution or Workaround
Ignore the on screen anomaly, as the symbol displays correctly when printed or exported. For example, this is the same area of the map from the map exported to PDF:
In this example, the hash line symbol has 1pt width and 1pt length. This symbol is indiscernible from a round or circle character marker symbol that is 1pt, so a different symbol should be used instead.