According to Apple's Bundle Programming Guide, an .app bundle plist is expected to contain the following keys:

CFBundleName
CFBundleDisplayName
CFBundleIdentifier
CFBundleVersion
CFBundlePackageType
CFBundleSignature
CFBundleExecutable

However a qmake-generated plist only contains:

CFBundleIdentifier
CFBundlePackageType
CFBundleSignature
CFBundleExecutable

The CFBundleVersion is particularly vital as it is the only way the OS has to identify versions for updates etc. But qmake does not create this, nor does it copy the VERSION variable to a template plist specified with QMAKE_INFO_PLIST.

Other keys that should be generated (or picked up in the case of QMAKE_INFO_PLIST) are CFBundleShortVersionString (used by the Finder) and LSMinimumSystemVersion (could be populated by QMAKE_MACOSX_DEPLOYMENT_TARGET).