Cannot login with Windows Authentication if users have similar names

Description

Steps to reproduce

1. Create a user in Windows named "user1".
2. Create another user in Windows named "user10".
3. Login with "user10." No problem.
4. Login with "user1." See error.

EPiServer.Data.Providers.SqlDatabaseHandler: Exception thrown while executing transaction

System.Data.SqlClient.SqlException (0x80131904): No user with username user1 was found
Cannot insert the value NULL into column 'fkSynchedUser', table 'intranet.dbo.tblSynchedUserRelations'; column does not allow nulls. INSERT fails.
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds, Boolean describeParameterEncryptionRequest)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite)
at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
at EPiServer.Data.Providers.SqlDatabaseHandler.<>c_DisplayClass32.<ExecuteTransaction>b_31()
at EPiServer.Data.Providers.SqlDatabaseHandler.<>c_DisplayClass35`1.<ExecuteTransaction>b_34()
at EPiServer.Data.Providers.SqlTransientErrorsRetryPolicy.Execute[TResult](Func`1 method)
at EPiServer.Security.SynchronizingUserService.SynchronizeUserAndClaims(String userName, IEnumerable`1 claims)
at EPiServer.Security.WindowsRoleProvider.GetRolesForUser(String username)
at System.Web.Security.RolePrincipal.IsInRole(String role)
at EPiServer.Security.MappedRole.IsInRoleOrVirtual(IPrincipal principal, Object context, String role)
at EPiServer.Security.MappedRole.IsInVirtualRole(IPrincipal principal, Object context)
at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at EPiServer.Security.VirtualRolePrincipal.IsInRole(String role, SecurityEntityType type, Object context)
at EPiServer.Security.VirtualRolePrincipal.IsInRole(String role)
at System.Web.Configuration.AuthorizationRule.IsTheUserInAnyRole(StringCollection roles, IPrincipal principal)
at System.Web.Configuration.AuthorizationRule.IsUserAllowed(IPrincipal user, String verb)
at System.Web.Configuration.AuthorizationRuleCollection.IsUserAllowed(IPrincipal user, String verb)
at System.Web.Security.UrlAuthorizationModule.CheckUrlAccessForPrincipal(String virtualPath, IPrincipal user, String verb)
at EPiServer.Security.PrincipalInfo.HasPathAccess(String path)
at EPiServer.Web.DisplayChannelService.GetActiveChannels(HttpContextBase context)
at EPiServer.Web.TemplateResolverImplementation.ResolveCore(HttpContextBase httpContext, ContentType contentType, Type itemType, Object itemToRender, TemplateTypeCategories category, String tag)
at EPiServer.Web.TemplateResolver.Resolve(HttpContextBase httpContext, Object itemToRender, TemplateTypeCategories templateTypeCategory, ContextMode contextMode)
at EPiServer.Web.Mvc.ExistingActionRouteConstraint.Match(Route route, SegmentContext routingContext, String parameterName)
at EPiServer.Web.Routing.ContentRoute.MatchConstraints(SegmentContext segmentContext, HttpContextBase context)
at EPiServer.Web.Routing.ContentRoute.GetRouteData(HttpContextBase httpContext)
at System.Web.Routing.RouteCollection.GetRouteData(HttpContextBase httpContext)
at EPiServer.Web.Routing.RouteCollectionExtensions.HandleRouteData(RouteCollection routes, HttpContextBase context)
at EPiServer.Global.DefaultDocumentHandling(Object sender, EventArgs e)
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
ClientConnectionId:d0fe5f30-d76f-4c0f-aebd-5487dbe4fdab
Error Number:50000,State:1,Class:16