Droppping a Foreign Key produces inconsistent results

[Duncan Jack]

I notice that using ALTER TABLE to drop a foreign key constraint removes the records from INFORMATION_SCHEMA.KEY_COLUMN_USAGE.

Sometimes, the index on the referencing column(s) seems to get "left behind", in other words an entry is created in the INFORMATION_SCHEMA.STATISTICS table when the foreign key is dropped.

I would understand this behaviour if it was consistent, what puzzles me is why it only happens sometimes. Any ideas, or should I investigate further to identify a pattern?

Duncan