FYI Actual version is 2.5.2 running on Linux RHE4.

>>> import struct
>>> fmt ='>f'
>>> v=1.8183e-7
>>> v
1.8183000000000001e-07
>>> s=struct.pack(fmt,v)
>>> struct.unpack(fmt,s)
(1.818300034983622e-07,)

Looks to me like the float->double conversion is not being zeroed out
before the 4 bytes are written to it.  FYI this is a fairly serious
issue since it leads to incorrect results be read from files (at least
for me anyway).