I don't really see this as a bug in the behaviour.  I'd always understood 
the purpose of the "at least one digit after the decimal" to be to make it 
possible to visually distinguish floats and integers, in the same way that 
repr and str already do.

>>> repr(1e100)
'1e+100'
>>> repr(1e5)
'100000.0'

If an exponent's present then the string's already clearly not an integer, 
so there's no need for the '.0'.