When I tag a face, one of the following happens:
- Digikam hangs. The trace shows memory exhaustion
- Digikam seems to run normally, but when I click on any other thumbnail, it will no longer show the enlarged picture (with message displayed in a small box: 'failed to load image').

I am now running V4.9, but the issue existed also in the previous versions (V4.8 and V4.5). My platform is Windows7, 64 bits

Reproducible: Always

Steps to Reproduce:
1. start Digikam
2. my photos are organised in directories per date
3. select a date (Album) and pick a thumbnail without face tag
4. on the picture, do the tagging, add name

Actual Results:  
hang or 'failed to load', as stated above
Sometimes the tag has been applied correctly (to be seen after restarting Digikam), sometimes the tag shows up (as shown under the thumbnail and in the tag list on the right of the screen) but the box around the face (that is the position of the face) has been lost

Expected Results:  
no hang, tag stored correctly

Logfile from DebugView:
00000001	0.00000000	[10192] QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave.	
00000002	0.14613296	[10088] digikam(10088)/phonon (KDE plugin): Can not create backend object from factory for  "VLC" ,  "phonon_vlc" :	
00000003	0.14613296	[10088]  "Could not find plugin 'VLC' for application 'digikam'" 	
00000004	0.14848362	[10088] WARNING: bool __thiscall Phonon::FactoryPrivate::createBackend(void) phonon backend plugin could not be loaded 	
00000005	0.15215798	[10088] digikam(10088)/phonon (KDE plugin): Can not create backend object from factory for  "VLC" ,  "phonon_vlc" :	
00000006	0.15215798	[10088]  "Could not find plugin 'VLC' for application 'digikam'" 	
00000007	0.15450543	[10088] WARNING: bool __thiscall Phonon::FactoryPrivate::createBackend(void) phonon backend plugin could not be loaded 	
00000008	0.91469908	[10088] digikam(10088)/phonon (KDE plugin): Can not create backend object from factory for  "VLC" ,  "phonon_vlc" :	
00000009	0.91469908	[10088]  "Could not find plugin 'VLC' for application 'digikam'" 	
00000010	0.91791570	[10088] WARNING: bool __thiscall Phonon::FactoryPrivate::createBackend(void) phonon backend plugin could not be loaded 	
00000011	0.92171711	[10088] digikam(10088)/phonon (KDE plugin): Can not create backend object from factory for  "VLC" ,  "phonon_vlc" :	
00000012	0.92171711	[10088]  "Could not find plugin 'VLC' for application 'digikam'" 	
00000013	0.92392439	[10088] WARNING: bool __thiscall Phonon::FactoryPrivate::createBackend(void) phonon backend plugin could not be loaded 	
00000014	0.92754161	[10088] digikam(10088)/phonon (KDE plugin): Can not create backend object from factory for  "VLC" ,  "phonon_vlc" :	
00000015	0.92754161	[10088]  "Could not find plugin 'VLC' for application 'digikam'" 	
00000016	0.92971945	[10088] WARNING: bool __thiscall Phonon::FactoryPrivate::createBackend(void) phonon backend plugin could not be loaded 	
00000017	0.92977971	[10088] WARNING: Phonon::createPath: Cannot connect  Phonon::MediaObject ( no objectName ) to  Phonon::AudioOutput ( no objectName ). 	
00000018	0.93327576	[10088] digikam(10088)/phonon (KDE plugin): Can not create backend object from factory for  "VLC" ,  "phonon_vlc" :	
00000019	0.93327576	[10088]  "Could not find plugin 'VLC' for application 'digikam'" 	
00000020	0.93550807	[10088] WARNING: bool __thiscall Phonon::FactoryPrivate::createBackend(void) phonon backend plugin could not be loaded 	
00000021	0.93556869	[10088] WARNING: Phonon::createPath: Cannot connect  Phonon::MediaObject ( no objectName ) to  Phonon::VideoWidget ( no objectName ). 	
00000022	0.93916571	[10088] digikam(10088)/phonon (KDE plugin): Can not create backend object from factory for  "VLC" ,  "phonon_vlc" :	
00000023	0.93916571	[10088]  "Could not find plugin 'VLC' for application 'digikam'" 	
00000024	0.94134450	[10088] WARNING: bool __thiscall Phonon::FactoryPrivate::createBackend(void) phonon backend plugin could not be loaded 	
00000025	2.27831221	[10088] QWindowsFileSystemWatcherEngine: unknown message '	
00000026	2.27899265	[10088] QWindowsFileSystemWatcherEngine: unknown message '	
00000027	2.30039787	[10088] QWindowsFileSystemWatcherEngine: unknown message '	
00000028	2.30041027	[10088] QWindowsFileSystemWatcherEngine: unknown message '	
00000029	60.38029480	[10088] qUncompress: could not allocate enough memory to uncompress data	
00000030	60.38037872	[10088] digikam(10088)/KFACE class KFaceIface::LBPHFaceModel __thiscall KFaceIface::TrainingDB::lbphFaceModel(void) const: Cannot uncompress histogram data to checkout from database for Identity  3 	
00000031	60.38051987	[10088] qUncompress: could not allocate enough memory to uncompress data	
00000032	60.38055801	[10088] digikam(10088)/KFACE class KFaceIface::LBPHFaceModel __thiscall KFaceIface::TrainingDB::lbphFaceModel(void) const: Cannot uncompress histogram data to checkout from database for Identity  4 	
00000033	60.38069534	[10088] qUncompress: could not allocate enough memory to uncompress data	
 (many lines omitted)
00001699	60.80585098	[10088] digikam(10088)/KFACE: Default exception from OpenCV 	
00001700	61.39314270	[10088] digikam(10088)/digikam (core): Failed to allocate chunk of memory of size 11059200 bad allocation 	
00001701	61.39896011	[10088] digikam(10088)/digikam (core): Failed to allocate chunk of memory of size 39923712 bad allocation 	
00001702	61.39944077	[10088] digikam(10088)/digikam (core) void __thiscall Digikam::PreviewLoadingTask::execute(void): Cannot extract preview for  "D:/Homegroup/Photos/2015/2015-02-03/P1020658.JPG" 	
00001703	61.39947128	[10088] digikam(10088)/digikam (core) void __thiscall Digikam::PreviewLoadingTask::execute(void): Cannot extract preview for  "D:/Homegroup/Photos/2015/2015-02-03/P1020658.JPG"