Two mated Docking Ports won't disconnect?

[_Zee]

My current project is building a low orbit space station. It is in the very earliest stages, and I've run into a problem.

I'm launching the pieces up one by one, and then using a "tug boat" to pick them off the launch craft, and then place the piece onto the station. I got the piece into place, but now I can't get the tug boat to disconnect from the piece that I've added to the station. If I try to disconnect the tub boat+solar array from the station, then it works just fine. But it won't allow me to simply remove the tug boat from the solar array. Clicking on the Undock button does nothing. Pic included. Thanks for your help.

[rryy]

This is a bug. Take a look here for a fix.

[Syhrus]

Must be something in the air, I just had this bug too... I fixed mine be undocking where it would let me, thrusting back slightly so the ports reset, then thrust forward and simultaneously undocked the other part. Fixed my problem.