PVS-Studio warning V560 for CxImage

void DCR_CLASS dcr_identify(DCRAW* p)
{
  ....
  if (--p->height == 2798 && (p->height = 2760))
    p->top_margin = 15;
  ....
}

This suspicious code was found in CxImage project by PVS-Studio static code analyzer.
Warning message is:
V560 A part of conditional expression is always true: (p->height = 2760). libdcr.c 7479

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/