NT151 Coupler : Unable to use maximum bytes in coupler variables.

Steps to reproduce:

1. Open the attached project.

2. Check the PROFINET IO sizes - its 1430/1024 and 1426/1024.

3. Try adding a new coupler variable.

Expected result:

A coupler variable should be added.

Current result:

A message is shown that the maximum is reached.

The max size for input and output in profinet should be 1432. Inputs have 4 bytes predefined which leaves 1428 that should come from the coupler variables.