The dialog component has changed behavior on me from UI 1.7.2 to 1.8rc3

1. $("#help_eff_date").dialog(
           {autoOpen: false, width: 350 , position: 'center' });
   
   

This used to give me a dialog centered as expected.

Running jquery 1.4.2 and UI 1.8rc3,  my dialog is left all the way to the left at the very bottom, immediately after the last markup for the entire page.

I've tried every which way of positioning my dialog, i.e.

1. ("#help_eff_date").dialog(
           {autoOpen: false, width: 350 , position: [300,200] });
   

But every time the position property seems to be ignored????? 

I've tried with two theme setups,  one an original 1.7.2 Theme that's always worked,  then one with a generic 18.rc3 theme.  They both exhibit the same problem, although the 1.8rc3 theme braks accordion headers, (see related post)

Under UI 1.7.2 my markup would center OR position the dialog,  under 1.8rc3 using the same markup it gets positioned as shown below: