Why is PC matrix multiplied by cdelt1 to get CD matrix

[mcara]

In pc2cd() function in hstwcs.py, conversion from PC to CD matrix is performed by multiplying PC matrix by cdelt[1], which is not what should be done mathematically:

stwcs/stwcs/wcsutil/hstwcs.py

Lines 467 to 469 in 440169c

	def pc2cd(self):
	if self.wcs.has_pc():
	self.wcs.cd = self.wcs.pc * self.wcs.cdelt[1]

What is the reason for this?

CC: @nden @stsci-hack