Why do you need to connect measure port when you flash XMEGA pinned to UFO board?

When I use CW1173 capture board and UFO target board (CW308-04) with XMEGA target board (CW308T-XMEGA-03) and try to flash target with XMEGAProgrammer class (with find/erase/program sequence), capture board’s ‘measure’ port has to be connected to UFO’s ‘VOUT’. Otherwise, “IOError: XMEGA Command 20 failed: err=3, timeout=1” error appears on erase. It doesn’t happen when I do it with STM target boards. It’s not a big problem but I was just wondering why it’s happening. What is ‘measure’ needed for in this case?

That is odd; I have the same board versions and I’m able to program the XMEGA with no measure port connected. Are you using the 20-pin cable?