I am not able to recreate your issue using the ExecuteNonReader. One thing that looks odd is this line:
$db.Create()
Why are you trying to create a new database? Maybe this is from you boiling down the code for us. For me that part broke my demo, but either way I have a file in it with the two INSERTS you showed and they were inserted into a table perfectly using the other code you showed.
There are no special teachers of virtue, because virtue is taught by the whole community.
--Plato