As a person who messes with SQL Server there is a pretty strong probability that you are using SQL Server Management Studio (SSMS). It is a very full featured tool, but does have a couple of problems and quirks (like crashing on large result sets due to it reaching the maximum memory allocation for a 32bit process).
The other day I came across another quirk, maybe even a bug, which can happen when returning and working with XML results, which could lead you to copy incorrect data…
SirSQL.net 