Problem: Merge does not correctly merge features when attribute table is open
This problem is addressed in ArcGIS 8.1 Service Pack 1. See Related Information section to download this pack.
When using the Merge command, while the attribute table is open, the selected features are not always merged as expected. A multi-part feature consisting of some of the selected features will result.
This is a known problem.
Solution or Workaround
Close the attribute table before attempting to merge the selected features.