Submit a bug to bugreport.apple.com: I sent this in earlier this year:

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04-Jan-2009 11:41 PM Sung Pae:
Summary:

Terminal.app incorrectly sets shell window dimensions on opening and closing tabs, resulting in a progressively smaller terminal window.

This problem is related to the application's recalculation of the window size when closing a tab, leaving only one tab open. If the tab bar is set to be hidden when unnecessary, the application's window size decreases by the size of the tab bar, but also resets the shell dimensions, shrinking the size of the window by one row.

Font and font-size settings affect this bug. Certain fonts and font-sizes do not change the shell window dimensions on tab close, but others do.


Steps to Reproduce:

Create a new Terminal window and change the default font to either:

Monaco 12pt
Courier 12pt

Other font/font-size combinations work too. Also, make sure that the tab bar is set to be hidden when there is only one tab open (Command-Shift-T toggles this setting).

Open one tab and then close it. Do it again repeatedly to watch the window shrink in size one line at a time.


Expected Results:

Hiding the tab bar should not have changed the shell window dimensions.


Actual Results:

When the tab bar disappears after the penultimate tab closes, the shell dimensions shrink by one row.


Regression:

This problem does not occur when using certain font/font-sizes (10pt Monaco and 10pt Courier for example). This issue can also be circumvented by showing the tab bar at all times.

The bug you reported seems to be identical to the one identified here. Maybe you meant to say "Don't bother submitting a bug report -- I already did it."?