Picklist alignment issue

We've noticed that if a picklist is the first column in an OpenUI list applet, the drop down for the picklist is displayed off of the left side of the browser window and not left aligned to the column control itself:

Where picklists are in other column locations in the applet, the drop down aligns itself correctly with the left edge of the column control:

I've looked at the CSS used but it seems to be generated 'on the fly' in order to try to align the columns. In the instance above, it's applying an inline attribute of "left: -16.5px", which is obviously not something I can see in the theme css.