lambdified sympy expression returns incorrect result

I encountered following problem, first I will explain briefly what is going on:

f(x)
g(x, y) = f(x) - y

From there we expect

g(x, f(x)) = f(x) - f(x) = 0

lambdified g(x,y) returns something very close to zero instead of zero. Here's a code that reproduces the problem. It arrives only when I put sufficient amount of log evaluations in f(x)

gist: https://gist.github.com/marekyggdrasil/39a24213ebaba6293464d116821cc334

source:

from sympy import Symbol, pprint, log, lambdify

# setting symbols
g1 = Symbol("gamma1")
g2 = Symbol("gamma2")
g3 = Symbol("gamma3")
g4 = Symbol("gamma4")
rt = Symbol("rt")

# setting expressions
criteria  = (g1 * log(g1, 2.0))/2.0
criteria += (g2 * log(g2, 2.0))/2.0
criteria += (g3 * log(g3, 2.0))/2.0
criteria += (g4 * log(g4, 2.0))/2.0
rooteq = criteria - rt

print "\ncriteria function: "
pprint(criteria)

print "\ncriteria function - rt: "
pprint(rooteq)

# lambdifying expressions to callable functions
tsymbols = [g1, g2, g3, g4, rt]
lambfun_criteria = lambdify(tsymbols, criteria)
lambfun_rooteq = lambdify(tsymbols, rooteq)

# example point x
x = [0.25006462253641376, 2.2501938662000542, 2.2501938662000542, 2.2501938662000542, 0.0]

# evaluating of criteria on x
rootval = lambfun_criteria(*x)

# setting rt to this evaluation
x[4] = rootval

print "\nactual evaluation of rooteq: " + str(lambfun_rooteq(*x))
print "\nexpected evaluation of rooteq: " + str(- x[4] + lambfun_criteria(*x))

output

$ python lambdifytest.py 

criteria function: 
0.721347520444482⋅γ₁⋅log(γ₁) + 0.721347520444482⋅γ₂⋅log(γ₂) + 0.721347520444482⋅γ₃⋅log(γ₃) + 0.721347520444482⋅γ₄⋅log(γ₄)

criteria function - rt: 
0.721347520444482⋅γ₁⋅log(γ₁) + 0.721347520444482⋅γ₂⋅log(γ₂) + 0.721347520444482⋅γ₃⋅log(γ₃) + 0.721347520444482⋅γ₄⋅log(γ₄) - rt

actual evaluation of rooteq: 4.4408920985e-16

expected evaluation of rooteq: 0.0