Excel Drop Down List Data Validation error in table

Hello, when making a drop down list in a table, I get a data validation error. Does anyone know how I can avoid this?
The problem arises when I'm inserting a different value than the ones available in the drop down list. I turned off the error warning in data validation options.
Using a drop down list outside a table environment works as expected.
I am using a curstom text format and using VBA to adjust the value in the drop down list.

Please find attached an illustration of the problem.
I would appreciate any help.

Thanks in advance,
Thomas