Unity 5.0.2f1 - Cannot debug with monodevelop

When pressing "Attach" in "Attach in Process" window, the button depressed for about 0.1 second and then returned to unpressed state even if I am still holding the mouse button, then nothing happened and debug didn't start.
I tried all of the things below and it still doesn't work:
1. both 32 and 64-bit Unity editor
2. checked editor settings in Preferences > External Tools
3. deleted all Unity and Monodevelop folders in Program Files and Appdata folders
4. deleted all Unity and Monodevelop entries in HKLM and HKCU
5. start a new empty project

PS: I can build the game and play in my phone, the only problem is I can't attach to process and thus cannot use breakpoints. Please help, thanks.

 

Unity 5.0.1f1 does not have this problem, therefore I submitted a bug report already.

 

No one have this problem? I also tried UnitySetup64-5.0.2p4 and this problem persists, in both win7x64 and win8.1x64

 

I still have this problem, with Unity 5.0 and Unity 5.1. There are a way to solve it?

 

I have this problem since upgrading to 5.0.2f1, and in build 5.1.1f1 which I got last night. I'm guessing the lack of response means it's something in our systems causing it. But it defo started with 5.0.2f1.

I am only able to attach by spam-clicking the attach button 3-15 times. then it attaches.

 

I solved it by double clicking the Process Name "xxxx Unity Editor (Unity)" in that window instead of clicking the Attach button.