It is happending to me also.

I have only tested this using Capsule.

Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: [Microsoft][SQL Server Native Client 11.0][SQL Server]A transaction that was started in a MARS batch is still active at the end of the batch. The transaction is rolled back.' in C:\caseon.dk\cn.new.caseon.dk\vendor\illuminate\database\Illuminate\Database\SqlServerConnection.php:15

Stack trace:
#0 C:\caseon.dk\cn.new.caseon.dk\vendor\illuminate\database\Illuminate\Database\SqlServerConnection.php(15): PDO->exec('BEGIN TRAN')
#1 [internal function]: Illuminate\Database\SqlServerConnection->transaction(Object(Closure))
#2 C:\caseon.dk\cn.new.caseon.dk\lib\Capsule\DB.php(24): call_user_func_array(Array, Array)
#3 C:\caseon.dk\cn.new.caseon.dk\ajax\discountGroupDetails.php(64): Capsule\DB::__callStatic('transaction', Array)
#4 C:\caseon.dk\cn.new.caseon.dk\ajax\discountGroupDetails.php(64): Capsule\DB::transaction(Object(Closure))
#5 C:\caseon.dk\cn.new.caseon.dk\controllers\frontController.php(32): discountGroupDetails->save()
#6 {main}
thrown in C:\caseon.dk\cn.new.caseon.dk\vendor\illuminate\database\Illuminate\Database\SqlServerConnection.php on line 15

I have a solution for this in pull #1883.

This should be fixed.