Limit generating an error

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SageMath return a strange error in evaluating the following limit.

var('x a b γ')
U_5 = lambda x, a, b, γ: ((1-γ)/γ)*(((a*x)/(1-γ))+b)^γ 
U_5(x, a, b, γ)
limU=lim(U_5(x, a, b, γ), γ=1)
show(LatexExpr(r"\lim_{\gama\rigtharrow 1}U_5(x, a, b, γ) = "),limU)

Incidently it's not a problem linked to unicode variables since I have the same result in substituting c for γ.

Here is the error message

ECL says: BINDING-STACK overflow at size 10240. Stack can probably be resized. Proceed with caution.

Incidently the result is well known (a linear function of x) and in one of my numerous essays I have had this result but changing the display I loose it and again I have the same error message..