Symptoms

Picker control does not wrap to the next line in 'Lithium' and 'SharePoint 2013' Themes.
 

Diagnoses

When viewing the computed styles of the innermost <div> (with role="textbox"), the 'Lithium' and 'Sharepoint 2013' themes appear to set 'white-space: nowrap'.

Resolution

Overriding the CSS 'white-space: normal' via <style> injection fixes the issue. Add the following text into an expression on a Data Label set to literal:

<style>.editable-area.input-control.styling-font {white-space:normal;}</style>