Edit, after the parent was edited to include the data attribute example:
You should update your post to clarify that you're talking about data attributes. That's a significant detail and shouldn't have been left out.
Now that you've clarified, jQuery does behave as you've stated, but it's not a bug. I can see how it could be unexpected behavior to some, but it's explicitly stated in the .data() documentation:
Every attempt is made to convert the string to a
JavaScript value (this includes booleans, numbers,
objects, arrays, and null) otherwise it is left as a
string. To retrieve the value's attribute as a string
without any attempt to convert it, use the attr() method.
A string of "1.410" is not the same as a float of 1.41. Running "1.410" full-circle through data() corrupts the input string. When you have data that has been entered by a user, you can't guarantee that it's not something that will happen to autoconvert.
This behavior is totally broken and should never be used. It will work 99.95% of the time, then fail in bizarre ways when a user types in something magic. These are the worst bugs in the world to hunt down. This really shouldn't be in jquery.
I can see why they would do this. Having to parseInt all default values wouldn't be very jQuery-like.
1.410 === 1.41
<div id="test" data-foo="1.1">
$('#test').data('bar', '1.1');
typeof $('#test').data('foo'); // number
typeof $('#test').data('bar'); // string
<div data-emoticon="0.0" /> elem.data('foo', { 'a':1, 'b':2 });
elem.data('foo'); // Returns the object
elem.attr('foo', { 'a':1, 'b':2 });
elem.attr('foo'); // Returns "[object Object]"
http://jsfiddle.net/kgp2H/
Think of it this way, say you have a template that is putting some data into an element like this:
<button id="fooButton" data-key="1.400">Click me to edit something</button>
Now, using .data() to select the information out, will always return 1.4 instead of what you want, which is 1.400.