Hey there!

I've started playing with operator's draw() and found some stuff...

Here is a simple operator: http://www.pasteall.org/19796/python

row= layout.split().row()
row.prop(self, 'use_temperature', text= "")
row.prop(self, 'temperature', text= "K")

If draw code is not finished with layout call (like layout.separator()) UI is trimmed - no OK button.
http://vray.cgdo.ru/tmp/screenshots/trim_ui.png

Here is a screenshot with layout.separator() at the end:
http://vray.cgdo.ru/tmp/screenshots/nontrim_ui.png

Also operator draw is not redrawn, so this code will never show 'temperature':
row= layout.split().row()
row.prop(self, 'use_temperature', text= "")
if self.use_temperature:
row.prop(self, 'temperature', text= "K")

Thanks in advance!

Best regards,
Andrey