When the mouse moves around the sheet, the preferences window and the spreadsheet will flicker with focus seeming to alternate between them.
The windows also come to the top: you can see this if you put another window in front of calc and then move over the calc window again while preferences is open.
To reproduce:
Setup autoraise for sloppy focus.
Open libre office calc.
Go to LibreOffice->Preferences.
When the mouse moves around the sheet, the preferences window and the spreadsheet will flicker with focus seeming to alternate between them.
The windows also come to the top: you can see this if you put another window in front of calc and then move over the calc window again while preferences is open.