Certainly sounds wrong from your description - personally I'd vote for breaking 
old code (with an appropriate notice in the version notes) unless you think a 
dictionary is actually a better solution. But I'd be interested to hear Lukas' 
opinion as to whether it was a bug or not...

Hi all. Just  for extend information about the bug, I copy here the email I 
sent yesterday to the list. 
http://forum.world.st/Incorrect-position-en-JQDialog-td4399806.html

I guess that the JQWDialog is inconsistent informing the position of dialog in 
position: and onDragStop: methods.
I check in Seaside-3.0.6-OneClick and 
http://jenkins.lukas-renggli.ch/job/Seaside%203.0/lastSuccessfulBuild/artifact/S
easide-3.0-OneClick.zip

To reproduce the problem:

1) Add position instance variable to JQUiFunctionalTest and modify 
>>renderWindowOn: to look like this :

script: (html jQuery new dialog
     position: position;      "line added"
    onDragStop: (html jQuery ajax callbackDraggable: [ :event |       " line added"
        position := (event at: #position). position inspect ]);      "line added"
     title: 'Vegetables';
    autoOpen: false;
    addButton: 'Close' do: html jQuery new dialog close);
    with: [ html unorderedList list: self vegetables ].

2) Go to http://localhost:8080/javascript/jquery-ui/dialogwidget
3) Press button Open Window and move de Dialog to bottom-left corner.
4) Refresh the page and press again button Open Window

The dialog show with de left-top attributes changed each other.

If you see the position in inspector that is opened when drag stop, the 
callbackDraggable: inform top@left, but in the comment of JQDialog>>position: 
method say that left@top are expected as parameter:
" 2) an array containing an x,y coordinate pair in pixel offset from left, top 
corner of viewport (e.g. [350,100]) "

The fact, if you change the coordinates of position with transposed the problem 
is solved:
onDragStop: (html jQuery ajax callbackDraggable: [ :event |
        position := (event at: #position) transposed. position inspect ]);

And the same problem in onResizeStop with the position (I have split the 
coordinates for size). Add width and height ivars and next code for reproduce 
problem:
 width: width;
 height: height;
 onResizeStop: (html jQuery ajax callbackResizable: [ :event | 
     position := event at: #position.
     width := (event at: #size) x.
     height := (event at: #size) y ]); 


I look at JQDialog API and I see that left@top that say in position: method is 
fine:
http://docs.jquery.com/UI/Dialog#option-position

Maybe the callbacks are bad for position?

Name: JQuery-UI-JohanBrichau.92
Author: JohanBrichau
Time: 19 October 2014, 7:50:33.534425 pm
UUID: 0ec8f821-5964-40c8-b889-9f79b1534bc5
Ancestors: JQuery-UI-JohanBrichau.91

callbacks that pass serialized event objects project (left,top) on (x,y) which 
is counter-intuitive (https://code.google.com/p/seaside/issues/detail?id=715)