Maybe this is a release issue, it worked on .25, upgraded to .26 and it seems not to work in this scenario:
I try a MT to MT speed test, get results just fine.
I dl the windows speed test client/server, and try to speed test (UDP) to same MT router. It errors out saying can’t connect.
I try the MT to MT speed test again, says can’t connect.
Maybe I’m doing something wrong, but it worked a couple days ago before the upgrade! 
–Brad
I also noticed that the windows client btest tool seems to be broke since going to 2.8.26. I’m getting the same cannot connect error when i try to test bandwidth with my laptop.
Eric
Well I can receive or do both way transfer. But not able to do just a transmit test since .26. Otherwise it is partially working.
Yes from the RouterOS I can not do a send test since 2.8.26. But the special windows btest client (the standalone windows program) doesn’t seem to work at all with a RouterOS btest server since the upgrade.
Eric