The bug can be reproduced like this:

- Launch the "Demo Application - Telerik UI for WinForms R1 2019 SP1" provided with the control suite.

- Choose "Explore all controls", "List control", "Settings"

- In the "Settings panel", set "Selection Mode" to "MultiSimple"

- In the "Themes" panel, choose "Office2013Light"

- click on the second item, then the third, then the fourth to select --> OK

- click on the second item to unselect it --> Not OK, the list isn't refreshed accordingly

- click on the third item to unselect it --> Not OK, the second item is properly unselected but the third one is still selected