[autocomplete] suggestion dropdown occupies entire width of browser in chrome and safari

I have tried the default styles that came with autocomplete. The problem exists even with that theme. This doesnt happen in FF 3.6, IE 8 or Opera 10.5.3. It does happen in Safari 4 and Chrome 4.
Strangely enough, at times if I delete a char or add a space and thus re trigger the suggestion menu, it works fine with the proper width. But it isnt consistent.
Isnt anyone else facing this problem?

The above pic is the remote caching jsonp demo from the jquery ui downloads running in Chrome.