OB-6 Desktop: Portamento modes FrA and FrT - do they work?

I'm not sure if it's a desktop module limitation or my inability to trigger the portamento, but the FrA and FrT modes don't seem to work, no matter if I'm playing the keys, or holding a note down and then pressing another. The regular Fr and Ft modes work great.

Am I "holding it wrong" or do these modes actually not do anything on the desktop module OB-6? Thanks!