Reviewing the code realised that this var was implicitly declared as global.

ernesto-jimenez · ernesto-jimenez · commit 9aa1a38a328c · 2011-02-16T22:22:28.000Z
diff --git a/js/jquery.mobile.navigation.js b/js/jquery.mobile.navigation.js
@@ -171,7 +171,7 @@
 		}
 
 		//base element management, defined depending on dynamic base tag support
-		base = $.support.dynamicBaseTag ? {
+		var base = $.support.dynamicBaseTag ? {
 
 			//define base element, for use in routing asset urls that are referenced in Ajax-requested markup
 			element: ($base.length ? $base : $("<base>", { href: docBase }).prependTo( $head )),

Original file line number	Diff line number	Diff line change
`@@ -171,7 +171,7 @@`
`171`	`171`	`}`
`172`	`172`
`173`	`173`	`//base element management, defined depending on dynamic base tag support`
`174`		`- base = $.support.dynamicBaseTag ? {`
	`174`	`+ var base = $.support.dynamicBaseTag ? {`
`175`	`175`
`176`	`176`	`//define base element, for use in routing asset urls that are referenced in Ajax-requested markup`
`177`	`177`	`element: ($base.length ? $base : $("<base>", { href: docBase }).prependTo( $head )),`