When I open my back patio sliding door the alarm panel displays Closed and Opened at the same time - Why?

A customer reported an issue where the alarm panel's 'Alarm Log' displayed both 'Opened' and 'Closed' at the same time when he opened the back patio door, even though it should have only displayed 'Opened'.

The customer had the entry sensor installed like this below.

We suggested to the customer to remove and install the sensor like this.

After the customer changed the position of the sensor, as shown below.  That solved the issue.  When the customer opened the patio door, the alarm panel alarm log only displayed 'Opened'.