Hi @ddamasceno,
thanks for reporting this, I was able to reproduce it. The technical explanation of the bug is that the table spec is created and saved when the preview in the dialog is created. Unless the path to the file that should be read is not changed, the spec is not re-calculated during node execution. We definitely need to fix this and it needs also be re-calculated if a config is changed that affects the spec.
A workaround that hopefully works for you - although not pretty and nice at all - is to also control the path via flow variable. During the configuration of the dialog, this path needs to be different than during the execution. This leads to re-calculation of the spec. Take a look at the String to Path (Variable) node, it might be helpful for you.
Could look e.g. like this: 
Let me know if you have any issues or questions regarding that workaround. I will let you know once this bug is fixed.
Best,
Simon
Edit: The issue has been fixed with a new option and the workaround is not required anymore, see below post.