In case anyone else comes across this problem or finds this otherwise useful, I think I was able to (sort of) figure out the discrepancy examining the .nib file.
Both files have two keys defined: maxSize (under com.apple.ibtool.document.localizable-all) and gMaxSize (under com.apple.ibtool.document.objects). In the working file both of these have a string setting of {480, 270}. In the nonworking file they had a string setting of {0, 0}. Apparently the default configuration of the working file was setting the maximum size of the window equal to zero. In Inspector the Window Template Size tab had the "Maximum Size" box checked but a "0" for both Width and Height. I clicked the box once to clear the check. Ran the Carbon Simulator again and the window resized properly without disappearing. When I rechecked the box, Inspector automatically filled in the Width and Height parameters with valid values of 480 and 270. I ran the Carbon Simulator again and it resized properly in accordance with the new maximum size constraint.
I don't fully understand the XML code in the .nib file but apparently the default setting for the maximum size of the window was being set to zero. The incorrect code appeared in the .nib file as follows (with non relevant lines deleted):
Code:
<key>com.apple.ibtool.document.localizable-all</key>
<dict>
<key>1</key>
<dict>
<key>maxSize</key>
<string>{0, 0}</string>
<key>com.apple.ibtool.document.objects</key>
<dict>
<key>1</key>
<dict>
<key>gMaxSize</key>
<string>{0, 0}</string>