Wow!  Hard-to-find bugs can really give you insight into how the .Net Framework works.  I recently just battled an elusive bug that turned out to be quite simple.  In a history table, I logged events.  Each event had a description that a user could type in.  Well, I noticed that longer descriptions were being cut off short.  I looked at the database and noticed that my nvarchar(50) field was the culprit.  So I just changed it to nvarchar(4000) to give the users the most flexibility.  I change the corresponding stored proc to mimic the new field length and then went to test the change.  No dice.  It still cut off my description.  What gives?

ADO.NET!!!  I use an ADO.NET command to call my stored procedure.  The description was being truncated in the ADO call.  I restarted the app, and it worked fine.  ADO caches information about sproc parameters, and I had to restart the app for that cache to be recreated with the new length.