In order to be able to relocate the Qt installation I have<qtdir>/bin/qt.conf with the content

[paths]
prefix = ..

This causes "idc.exe foo_release.dll /idl foo_release.idl -version 1.0" to crash on exit with the following runtime exception: "Unhandled exception at 0x72d09036 (QtCore4.dll) in idc.exe.4324.dmp: 0xC0000005: Access violation reading location 0x7117ae14." with the following stack:

> QtCore4.dll!QVariant::~QVariant() Line 1412 + 0x6 bytes C++
QtCore4.dll!QMap<QSettingsKey,QVariant>::freeData(QMapData * x=0x00659070) Line 652 + 0x8 bytes C++
QtCore4.dll!QConfFile::~QConfFile() Line 233 + 0x76 bytes C++
QtCore4.dll!QCache<QString,QConfFile>::clear() Line 139 + 0x20 bytes C++
QtCore4.dll!QGlobalStaticDeleter<QCache<QString,QConfFile> >::~QGlobalStaticDeleter<QCache<QString,QConfFile> >() Line 1950 + 0x1b bytes C++
QtCore4.dll!_CRT_INIT(void * hDllHandle=0x0065b94c, unsigned long dwReason=6666424, void * lpreserved=0x0065b8b8) Line 415 C
QtCore4.dll!__DllMainCRTStartup(void * hDllHandle=0x72bc0000, unsigned long dwReason=929984518, void * lpreserved=0x00659080) Line 526 + 0x8 bytes C
QtCore4.dll!_DllMainCRTStartup(void * hDllHandle=0x72bc0000, unsigned long dwReason=0, void * lpreserved=0x00000001) Line 476 + 0xe bytes C
ntdll.dll!_LdrpCallInitRoutine@16() + 0x14 bytes
ntdll.dll!_LdrShutdownProcess@0() + 0x141 bytes
ntdll.dll!_RtlExitUserProcess@4() + 0x74 bytes
kernel32.dll!75ad79c5()
msvcr100.dll!___crtExitProcess() + 0x17 bytes
msvcr100.dll!__cinit() + 0xb689 bytes
msvcr100.dll!_exit() + 0x11 bytes
idc.exe!__tmainCRTStartup() Line 572 C

This only happens if foo_release.dll is a release build - not if it is a debug build.

The problem is reproducible with e.g qt\examples\activeqt\multiple. Simply drop in the qt.conf file from above in the bin folder where idc.exe lives and build the example as release.