Actually, I could be wrong. I just redownloaded your original file, and the Data Entry is not behaving correctly even if I don't use the Search button. I'll keep checking though...
Okay, just as an experiment, please check out the attached.
If you open the form, you'll see I moved your subform out of the tab control, just to see if the tab control was causing the problem. Don't use the search feature; instead, just use the navigation button and move through the next records.
When that didn't work out as expected, I created a new subform to see if the problem is with the subform and placed it to the right of the first one. You'll see that they both behave the same way.
Then, I created a new main form to see if the problem is with the main form, since I didn't see any code behind the main form that could be causing the problem. So, open up Form1, and you will see that the new subform is behaving correctly.
Then, as a final experiment, I added your original subform to the bottom of this new form. You will notice it also behaves normal, not like how it behaves when on your original main form.
As a conclusion, it's possible your main form is corrupted.
Hope that helps...