Run Terminal Command from .terminal file
In the .terminal file, RunCommandAsShell should not be set to &lt;true/&gt;.

This correlates to the "Run inside shell" checkbox in the "Shell" section of the preference window; which is more intuitively named.

When the preference is not selected (RunCommandAsShell is true), then the default shell is replaced with whatever command you've used.  If the preference is selected (RunCommandAsShell is either false or not listed in the .terminal file), then the command is run after the default shell is loaded for that Terminal window/tab.