[LAU] MIDI active sensing- USB midi and EvoMK461

I have just received the usb midi adapter I bought on ebay. I plugged it in and it was recognized immediately- it shows up in lsusb as: Bus 002 Device 014: ID 4348:552d Anyway- if I plug it into my ordinary keyboard or the midi out on my Evolution MK461 then it's very slow and frequently stops and/or plays the wrong notes- theres usually note 0 (very low) attached to any note I get from it. Sending it to aseqdump gives lots of "Active sensing" messages. I don't get these from the MK461s own USB, nor from the old gameport midi adapter I have. Also, key releases on these appear as midi events with note velocity 0, whereas they don't with the usb midi adapter. My first instinct was that USB1 is too slow and it needs USB2, but my MK461 works fine so why would this be any different? The funny thing is- if I select the "midi out from USB" setting on my MK and then route midi events from vkeybd to the MK (which then sends them back through the USB midi adapter plugged into the midi out) then it works as expected, even though the MK itself going through this line does not. Any ideas? Thanks Simon