deployment-target ignored during build, breaking iOS 7 support

Regardless of whether I set the "deployment-target" preference in config.xml, Cordova builds an app that requires a minimum of iOS 8.0. As a result, I can no longer build apps for iOS 7.

Create a new cordova project, and add to its config.xml:

<engine name="ios" spec="~4.1.0" />
<preference name="deployment-target" value="7.0" />

Run cordova prepare --verbose and cordova build. During the prepare phase, I see this message (three times, for some reason):

Set IPHONEOS_DEPLOYMENT_TARGET to "7.0".

And if I open the app in Xcode, it shows "Deployment Target" set to 7.0.

But the resulting .app file's Info.plist contains:

<key>MinimumOSVersion</key>
<string>8.0</string>

So I can't install it on iOS 7; I get this error on the device:

 installd[551] <Error>: 0x10050c000 verify_bundle_metadata: The system version is lower than the minimum OS version

This is still the case if I set "deployment-target" to 9.0.

This seems to be because cordova/build.xcconfig includes the line:

IPHONEOS_DEPLOYMENT_TARGET = 8.0