Problem Details:
So what the bug actually does is that when you press K1 or K2 while your cursor is on top of a player in the player list it will open up the player menu and your letter which K1/K2 is binded will be typed.

This bug has been bothering me for a good 2+ months while i was trying to type in chat and the player menu would pop up and i was randomly opening up chats / (un)friending people etc. but today i finally found out how to reproduce it.

These are the steps to reproduce it:

1. Go to the song list and have a song ready to play ( preferably a map with a long intro [ atama no taisu as used in the video ] coz the game will be paused when the 1st note comes up and the bug wont work.
2. Press f8 to open up the player list and move your cursor on top of a player. ( DO NOT MOVE YOUR CURSOR AT ALL NOW, dont touch the mouse/stylus )
3. Press f8 to close the player list and press enter to start the map.
4. Now while the map intro is playing Alt+tab out of osu and Alt+tab back in.
5. Press f8 to open up the player list ( i hope that cursor hasn't moved a pixel)
6. Press any key you have binded K1/K2 to and the player menu should pop up.

Some extra notes.
1. I use Win 8.1 x64 . Also tested on Win 8.0 x64 and still works
2. Osu Stable version
3. The bug works on fullscreen/Windowed/Bordless
4. In step 4-5 it doesnt matter if you open up the player list before or after you alt+tab
5. If you move your cursor the bug will go away but if you alt+tab out and back in it will reappear and work on the place you have the cursor on.
6. The bug will keep working until the song intro keeps playing and the game is not paused ( as said in step #1)
7. Tested on Win 7 but it doesn't seem to work. Feel free to try if you got Win 7 to make sure it doesn't.

Video or screenshot showing the problem:


osu! version: 20150414.2 (latest)

I am mind boggled to how people come across these things, but... I can confirm that after doing the following steps, the k1/k2 binded keys trigger the player options menu:

• 1) At ANY point while playing the map, alt+tab out and back in.
  
  2) This bug triggers only if the cursor is in the original location where the game got paused. This does mean that you can move the mouse all you want, go back to that one location and trigger the bug. I used the gamemode indicator of one of the players in the player list as a reference point.
  
  3) If the pause menu appears, press esc to get rid of it.
  
  4) Press the binded key to bring up the player list
  
  5) Spam your k1/k2 binded keys

Notes:

• - I think the pause menu nullifies the bug due to the fact osu! only applies the k1/k2 binded keys while playing the map
  
  - The cursor's bounding box of triggering this bug is the size of the "click area" bounding box of the orange unpause target.
  
  - While the orange target maybe on position x,y on screen, alt-tabbing out and back in seems to create an invisible target needed that triggers this bug. So go ahead and alt-tab in and out as many times as you want to give this "invisible target" a new location.
  
  - Win 8.1
  
  - osu! version: latest stable

Confirming...

Edit: Moving to low priority.