What steps will reproduce the problem?
1.output a floating point number such as 1 + eps

What version of the product are you using? On what operating system?
0.3.0, affects 0.5.0 too

What is the expected output? What do you see instead?
A number that when parsed yields the same value that was converted, instead a 
different number is yielded.

See this or many other threads for detail:
http://stackoverflow.com/questions/4738768/printing-double-without-losing-precis
ion

The executive summary is that digits10 is truncating the fractional digits a 
floating point number has and the round-trip output-input will be different in 
many cases.  You should instead clamp at digits10+1 and arguably set the 
defaults to be fully preserving as well to minimize surprises.  Patch attached 
that does this.  Alternatively use/implement David Gay's algorithm to convert 
to the shortest string which yields the same value could be used to keep yaml 
files small, preserve readability and what the computer actually had in memory 
at time of serialization.

http://www.ampl.com/REFS/rounding.pdf
David Gay's implementation:
http://www.netlib.org/fp/dtoa.c
http://www.netlib.org/fp/g_fmt.c

Apparently it is used all over the place (python, numerous web-browsers and 
popular databases) so it seems this is the defacto way to do it.

You may also want to use C/C++ strtod on input, which again likely borrows much 
of David's code as iostreams don't handle numerous cases, in particular 
denormed values (you likely already handle nan/inf)

http://www.cplusplus.com/reference/cstdlib/strtod/
http://www.cplusplus.com/reference/string/stod/