I made a simple mock up in SuperStore, but I was not able to recreate the problem.
I may not have adequately simulated your fields.
Would be grateful if you would adjust the attached workbook to match your setup.
235947trend.twbx 1.2 MB
Interesting, I have created a csv out of the original data - exact copy - and tried the same thing with that and it works as you say. It works as it should.
I have checked with your data, but could not find a way to modify to this result.
Now with the above, this gets really interesting...?
Any suggestions what settings I should check in Tableau Desktop?
Hmm. For the twb that doesn't work, what is your datasource?
Is it SQL Server?