Are there any known (documented?) restrictions for the use of the WolframAlpha function in CDF-Player and PlayerPro?

I only found a page which mentions upper values for various license version, but it doesn't explicitly mention the two player variants but only "other licenses".

Background: When I try a call to WolframAlpha in PlayerPro it just hangs with no message, even with the TimeConstraint option set to a low value. At least the TimeConstrained wrapper does work as it should. Of course I tested that the exact same code works without problems in Mathematica on the same machine. So I suspect that there are such restrictions but find it hard to find out what these are...