Opening boards manager causes duplicate "Recently used boards" items

[per1234]

Arduino IDE 1.9.0-beta build 107

1. Tools > Board
2. Note the number of entries in the "Recently used boards" section of the menu:
   
3. Tools > Board > Boards Manager
4. Click the "Close" button.
5. Tools > Board

There are now two additional copies of the selected board in the "Recently used boards" section of the menu: