4.5.3.2 fails to read long data type custom properties

[Texbase]

We migrated from 4.1.1.0 to 4.5.3.2 and can no longer read custom properties that are Int64/long data types.

On creation of the Excel file:
package.Workbook.Properties.SetCustomPropertyValue("Timestamp", DateTime.Now.Ticks);

On reading of the Excel file (with changes to the Excel file):
DateTime timestamp = new DateTime(Convert.ToInt64(package.Workbook.Properties.GetCustomPropertyValue("Timestamp")));

Always results in null, even though the CustomPropertiesXml contains a valid value:

<property name="Timestamp" pid="10" fmtid="{D5CDD505-2E9C-101B-9397-08002B2CF9AE}">
 <vt:r8>6.37115722044558E+17</vt:r8>
</property>

DotNetFiddle:

using System;
public class Program
{
	public static void Main()
	{
		Console.WriteLine(new DateTime(Convert.ToInt64(6.37115722044558E+17)));
		// returns 12/10/2019 10:56:44 AM		
	}
}

If we create the Excel file and immediately try to read it (without making any changes to it), the custom property is read successfully.