imenu-list is not updated when change buffer if point position is the same across buffers

[bitterfox]

How to reproduce

• Open 2 files with the same location of point
  • 
  • above example opens imenu-list.el and imenu.el.gz, point is heaf of file in both buffer
  • active buffer is imenu-list.el
• Open imenu-list
  • 
  • imenu-list shows the imenu of current buffer (imenu-list.el)
• Switch buffer to different buffer
  • switched to imenu.el.gz
  • Actual

    • 

    • imenu-list is not updated and still show imenu for the previous buffer(imenu-list.el)

  • Expected
    •