Thanks for reporting this. The issue has been logged as:
SPR#MKEE9M8HJL XPages Extlib, Value Picker control, “for” property does not allow choose Dojo List Text Box
and is likely to be fixed in the next openNTF release (901v08).
There's a workaround; to manually type for=“djextListTextBox1” into the XPage source tab,
instead of using the Properties view.