This bug is upstream bug #134 [1]. I've attached the patch that fixed it and also tested it working.
[1] http://bugzilla.rawstudio.org/show_bug.cgi?id=134
Index: src/rawstudio.c =================================================================== --- src/rawstudio.c (revisione 1440) +++ src/rawstudio.c (revisione 1441) @@ -648,13 +648,13 @@ rs_photo_open_dcraw_apply_black_and_shift_mmx(dcraw_data *raw, RS_PHOTO *photo) { char b[8]; - gushort *sub = (gushort *) b; + volatile gushort *sub = (gushort *) b; void *srcoffset; void *destoffset; guint x; guint y; gushort *src = (gushort*)raw->raw.image; - gint64 shift = (gint64) (16.0-log((gdouble) raw->rgbMax)/log(2.0)+0.5); + volatile gint64 shift = (gint64) (16.0-log((gdouble) raw->rgbMax)/log(2.0)+0.5); sub[0] = raw->black; sub[1] = raw->black;