Labels in TikZ are incorrectly interpreted

I'm running into a weird problem with TikZ. The following code

\node (A) [label=45:$A$] at (p2) {};

is rendered correctly in one document, but incorrectly in another, larger document (which uses incidentally more packages, this is why I suspect some package clash.

Surprisingly, the label specified by the portion of the code 45:$A$ is rendered explicitly as 45:A, rather than being interpreted as A at 45°. There is no warning or error raised.

Any idea of where the problem might come from?

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Welcome to TeX.sx! Please add a minimal working example (MWE) that illustrates your problem. You don't have to sign with your name since it automatically appears in the lower right corner of your post. – egreg Sep 20 '11 at 21:00
Do you compile the two documents on the same machine? Are are there potentially different versions of TikZ in play? – Caramdir Sep 20 '11 at 21:01