|   | 1 |  initial version  | 
Works for me in Sage 9.3.
Example:
sage: A.<x, y> = AffineSpace(QQ, 2)
sage: A
Affine Space of dimension 2 over Rational Field
sage: C = Curve(x^2 + y^2 -1)
sage: C
Affine Plane Curve over Rational Field defined by x^2 + y^2 - 1
Did you happen to redefine Curve earlier in your code?
Can you observe the problem in a fresh Sage session?
Do you have things in your init.sage file?
Does the problem persist after
sage: reset('Curve')
Same questions with AffineSpace.
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                Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.