ASSERT failure in QList<T>::at: "index out of range" on qmake process.

QMAKE_LFLAGS_X86_64 += FOO -Xarch_x86_64

greaterThan(QT_MAJOR_VERSION, 4) {
   QT += widgets
}

SOURCES = FooApp.cpp main.cpp
HEADERS = FooApp.h

qts-MacBook-Pro:fooapp qt$ ../qt-everywhere-commercial-src-4.8.4-build/bin/qmake -v
QMake version 2.01a
Using Qt version 4.8.4 in /Users/qt/Downloads/qt-everywhere-commercial-src-4.8.4-build//lib
qts-MacBook-Pro:fooapp qt$ ../qt-everywhere-commercial-src-4.8.4-build/bin/qmakeWARNING: Failure to find: FooApp.cpp
WARNING: Failure to find: main.cpp
WARNING: Failure to find: FooApp.h
ASSERT failure in QList<T>::at: "index out of range", file /Users/qt/Downloads/qt-everywhere-commercial-src-4.8.4-build/include/QtCore/../../../qt-everywhere-commercial-src-4.8.4/src/corelib/tools/qlist.h, line 447
Abort trap: 6
qts-MacBook-Pro:fooapp qt$

qts-MacBook-Pro:fooapp qt$ gdb ../qt-everywhere-commercial-src-4.8.4-build/bin/qmake
GNU gdb 6.3.50-20050815 (Apple version gdb-1822) (Sun Aug  5 03:00:42 UTC 2012)
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin"...Reading symbols for shared libraries ...... done

(gdb) run
Starting program: /Users/qt/Downloads/qt-everywhere-commercial-src-4.8.4-build/bin/qmake
Reading symbols for shared libraries +++++................................................................................................. done
WARNING: Failure to find: FooApp.cpp
WARNING: Failure to find: main.cpp
WARNING: Failure to find: FooApp.h
ASSERT failure in QList<T>::at: "index out of range", file /Users/qt/Downloads/qt-everywhere-commercial-src-4.8.4-build/include/QtCore/../../../qt-everywhere-commercial-src-4.8.4/src/corelib/tools/qlist.h, line 447

Program received signal SIGABRT, Aborted.
0x00007fff89268212 in __pthread_kill ()
(gdb) bt
#0  0x00007fff89268212 in __pthread_kill ()
#1  0x00007fff8af72af4 in pthread_kill ()
#2  0x00007fff8afb6dce in abort ()
#3  0x00000001003ec6f9 in qt_message_output (msgType=QtFatalMsg, buf=0x1028467f8 "ASSERT failure in QList<T>::at: \"index out of range\", file /Users/qt/Downloads/qt-everywhere-commercial-src-4.8.4-build/include/QtCore/../../../qt-everywhere-commercial-src-4.8.4/src/corelib/tools/qli"...) at qglobal.cpp:2301
#4  0x00000001003ec856 in qt_message (msgType=QtFatalMsg, msg=0x1005e92d0 "ASSERT failure in %s: \"%s\", file %s, line %d", ap=0x7fff5fbfe190) at qglobal.cpp:2347
#5  0x00000001003eca94 in qFatal (msg=0x1005e92d0 "ASSERT failure in %s: \"%s\", file %s, line %d") at qglobal.cpp:2530
#6  0x00000001003ecaf2 in qt_assert_x (where=0x1005dc158 "QList<T>::at", what=0x1005eb880 "index out of range", file=0x1005de5e0 "/Users/qt/Downloads/qt-everywhere-commercial-src-4.8.4-build/include/QtCore/../../../qt-everywhere-commercial-src-4.8.4/src/corelib/tools/qlist.h", line=447) at qglobal.cpp:2004
#7  0x00000001001885f7 in QList<QString>::at (this=0x10280ed48, i=7) at qlist.h:447
#8  0x0000000100157074 in UnixMakefileGenerator::processPrlFiles (this=0x102809050) at unixmake.cpp:644
#9  0x00000001000722e8 in MakefileGenerator::setProjectFile (this=0x102809050, p=0x7fff5fbff768) at makefile.cpp:291
#10 0x00000001001dc1c9 in MetaMakefileGenerator::createMakefileGenerator (proj=0x7fff5fbff768, noIO=false) at metamakefile.cpp:480
#11 0x00000001001d90f1 in BuildsMetaMakefileGenerator::init (this=0x102813870) at metamakefile.cpp:118
#12 0x00000001001dae68 in MetaMakefileGenerator::createMetaGenerator (proj=0x7fff5fbff768, name=@0x7fff5fbff8e8, op=false, success=0x7fff5fbff71f) at metamakefile.cpp:496
#13 0x0000000100052829 in runQMake (argc=1, argv=0x7fff5fbffaf0) at main.cpp:152
#14 0x0000000100053300 in main (argc=1, argv=0x7fff5fbffaf0) at main.cpp:174
(gdb) quit
The program is running.  Exit anyway? (y or n) y
qts-MacBook-Pro:fooapp qt$

qts-MacBook-Pro:fooapp qt$ ../../QtCommercial5.0.0/5.0.0/clang_64/bin/qmake -v
QMake version 3.0
Using Qt version 5.0.0 in /Users/qt/QtCommercial5.0.0/5.0.0/clang_64/lib
qts-MacBook-Pro:fooapp qt$
qts-MacBook-Pro:fooapp qt$ ../../QtCommercial5.0.0/5.0.0/clang_64/bin/qmake -v
QMake version 3.0
Using Qt version 5.0.0 in /Users/qt/QtCommercial5.0.0/5.0.0/clang_64/lib
qts-MacBook-Pro:fooapp qt$ ../../QtCommercial5.0.0/5.0.0/clang_64/bin/qmake
WARNING: Failure to find: FooApp.cpp
WARNING: Failure to find: main.cpp
WARNING: Failure to find: FooApp.h
qts-MacBook-Pro:fooapp qt$