All transactions now fall through to MSDTC when used with TransactionScope. Use the LocalTransactionScope to use local transactions and bypass MSDTC.
IMPORTANT: This is a breaking change as of release 220.127.116.11. Connections are now NOT implicitly opened when any any Database.ConnectionController.Execute* function is called within a TransactionScope. Instead a ConnectionScope must also be used to call the Execute* statement. Previously, the connection would be implicitly opened if any Database.ConnectionController.Execute* functions was called within a TransactionScope using statement. Normal calls to DatabaseObject.Save or Database.ObjectSave are not affected, so only minor code changes (if any) should be required.