Index: ui/ui.slider.js
===================================================================
--- ui/ui.slider.js	(revision 4895)
+++ ui/ui.slider.js	(working copy)
@@ -237,8 +237,17 @@
 			if(handle == undefined && !this.currentHandle && this.handle.length != 1) return false; //If no handle has been passed, no current handle is available and we have multiple handles, return false
 			if(handle == undefined && !this.currentHandle) handle = 0; //If only one handle is available, use it
 			if(handle != undefined) this.currentHandle = this.previousHandle = $(this.handle[handle] || handle);
-
-			if(value.constructor == String) value = /\-\=/.test(value) ? this.value() - parseInt(value.replace('-=', ''),10) : this.value() + parseInt(value.replace('+=', ''),10);
+	
+			if(value.constructor == String) {
+				if (/^\-\=/.test(value) ) {
+					value = this.value() - parseInt(value.replace('-=', ''), 10)
+				} else if (/^\+\=/.test(value) ) {
+					value = this.value() + parseInt(value.replace('+=', ''), 10)
+				} else {
+					value = parseInt(value, 10);
+				}
+			}
+			
 			if(o.stepping) value = Math.round(value / o.stepping) * o.stepping;
 			value = this.translateValue(value);