This bug is not reproducible in 10.5 or 10.5.1. No additional service packs are in the current product plan for ArcMap 10.3.1.
解决办法
Workaround 1: Set the field length to the exact length required for the final values.Workaround 2: Use data from an Oracle database.Workaround 3: Use ArcGIS for Desktop 10.4.1 or 10.5.