Can't open dockable dialogues if I close them and other strange behaviours

Ubuntu 11.10
GIMP 2.6.11

Problem with dockable dialogues (windows).

Steps to reproduce:
1. Start GIMP
2. Drag and drop tab with brushes (for example) somewhere
3. Close created window with brushes
4. Go to menu: Windows->Dockable dialogues->Brushes or Ctrl+Shift+B

Expected result:
Window with brushes appears

Result in my case:
Nothing happen

Problem with duplicating resources (I thing it goes together with above).

Steps to reproduce:

1. Start GIMP
2. In Gradients (for example) tab click icon “New gradient”
3. Close window which appeared
4. Click the icon again

Expected result:
The window appears again

Result in my case:

Gradient is duplicated every time I click “New gradient” icon.

Screencast attached.