This is because of $ContextPath. If the symbol outside the Begin/End is created in a context that is listed in $ContextPath, Mathematica will recognize it as belonging to that context even when called from a different context (even if Begin/End is put in a package file and called via Get):

$ContextPath

{"DocumentationSearch`", "ResourceLocator`", "PacletManager`",
 "QuantityUnits`", "WebServices`", "System`", "Global`"}

WebServices`x;
Begin["temp`"];
Print@Context@x;
End[];

 WebServices`

Now if I remove "WebServices`" from $ContextPath:

$ContextPath = DeleteCases[$ContextPath, "WebServices`"];
WebServices`x;
Begin["temp`"];
Print@Context@x;
End[];

temp`

No what has changed in related code in successive versions, I have no idea.

This is because of $ContextPath. If the symbol outside the Begin/End is created in a context that is listed in $ContextPath, Mathematica will recognize it as belonging to that context even when called from a different context (even if Begin/End is put in a package file and called via Get):

$ContextPath

{"DocumentationSearch`", "ResourceLocator`", "PacletManager`",
 "QuantityUnits`", "WebServices`", "System`", "Global`"}

WebServices`x;
Begin["temp`"];
Print@Context@x;
End[];

 WebServices`

Now if I remove "WebServices`" from $ContextPath:

$ContextPath = DeleteCases[$ContextPath, "WebServices`"];
WebServices`x;
Begin["temp`"];
Print@Context@x;
End[];

temp`

Now what has changed in related code in successive versions, I have no idea.