Error "Invalid URL: QUrl" while saving LDR-Images

Statistically - every third to fifth time - luminance-hdr freezes completly while saving a ldr-image. The dialog for selecting the target directory an filename does not appear.

System is Archlinux with KDE 5.4, but happend under KDE 5.3 too.

When starting the program on the console the following output is shown:

I18NDIR: /usr/share/luminance-hdr/i18n
QLibraryInfo::location(QLibraryInfo::TranslationsPath)): "/usr/share/qt/translations"
Database opened
KSambaShare: Could not find smb.conf!
kf5.kio.core: KLocalSocket(0x2bbfb40) Jumbo packet of 81880 bytes
kf5.kio.core: KLocalSocket(0x2bbfb40) Jumbo packet of 108884 bytes
[gamma0: 0.416667, gamma1: 12.92, 4-Color RGB: 0, Fuji Rotate: -1, User Quality (Demosaicing method): 10, Median Filter Passes: 0, WB Method: 1, WB Temp: 6500, WB Green: 1, Highlight Method: 0, Highlight Rebuild: 0, Black Level: N/A, Saturation: N/A, Auto Brightness: 0, Auto Brightness Threshold: 0.001, Brightness: 1, Noise Reduction: ON, Noise Reduction Threshold: 100, Chromatic Aberation: 0]
Data size: 108618048 108618048
W: 5208 H: 3476
MainWindow::updateActions( 0 )
pfstmo_mantiuk08 (saturation factor: 1, contrast enhancement factor: 1, white_y: -2, setluminance: 0)
Display function: gamma-gain-black-ambient
gamma = 2,2 L_max = 200 L_black = 0,8
E_amb = 60 k = 0,01
Display size paramaters:
pixels per visual degree = 30
viewing distance = 0,5 [meters]
pfstmo_mantiuk08: warning - wrong WHITE_Y in the input imageLuminance factor of the reference white: not specified

pde residual error: 0,000014
pfstmo_drago03 (bias: 0.85)
pfstmo_reinhard05 (brightness: -10, chromatic adaptation: 0, light adaptation: 1)
pfstmo_pattanaik00 (local: 0, multiplier: 1, Acone: 500, Arod: 500, autolum: 1)
pfstmo_mantiuk08 (saturation factor: 1, contrast enhancement factor: 1, white_y: -2, setluminance: 0)
Display function: gamma-gain-black-ambient
gamma = 2,2 L_max = 200 L_black = 0,8
E_amb = 60 k = 0,01
Display size paramaters:
pixels per visual degree = 30
viewing distance = 0,5 [meters]
pfstmo_mantiuk08: warning - wrong WHITE_Y in the input imageLuminance factor of the reference white: not specified

pde residual error: 0,000014
pfstmo_drago03 (bias: 0.85)
pfstmo_reinhard05 (brightness: -10, chromatic adaptation: 0, light adaptation: 1)
pfstmo_pattanaik00 (local: 0, multiplier: 1, Acone: 500, Arod: 500, autolum: 1)
TonemappingPanel::updateTonemappingParams(TonemappingOptions opts)
Monitor profile: ""
Printer profile: ""
MainWindow::updateActions( 1 )
Monitor profile: ""
Printer profile: ""
Invalid URL: QUrl("IMG_3019_pregamma_1_mantiuk06_contrast_mapping_0.1_saturation_factor_0.8_detail_factor_0.8.jpg")
kf5.kio.core: KLocalSocket(0x2a513e0) Jumbo packet of 32900 bytes
kf5.kio.core: KLocalSocket(0x2d12370) Jumbo packet of 32900 bytes
Invalid URL: QUrl("IMG_3019_pregamma_1_mantiuk06_contrast_mapping_0.1_saturation_factor_0.8_detail_factor_0.8.jpg")
TonemappingPanel::updateTonemappingParams(TonemappingOptions opts)
pfstmo_drago03 (bias: 0.85)
Monitor profile: ""
Printer profile: ""
No node found for item that was just removed: QUrl("file:///home/sebastian/Bilder/2015/2015-08-30 Birkkarspitze/IMG_6207_pregamma_1_mantiuk06_contrast_equalization_0.1_saturation_factor_0.8_detail_factor_1-1.jpg.out.pp3")
Invalid URL: QUrl("IMG_3019_pregamma_1_drago_bias_0.85.jpg")
Invalid URL: QUrl("IMG_3019_pregamma_1_drago_bias_0.85.jpg")