When you hide the form it will stay in memory until the application is closed.
May be it is an option to transfer the value from the textbox to the variable vTestProperty in the Change event. You can use the property to query it.
oMyDLL = CreateObject("mydll.mydllutil")
oMyDLL.TestProperty = Me.Text1
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'C' is shorthand for Confusion, 'C++' much more confusion...