Perky: Alerts do not disappear when they are no longer valid and can appear duplicated

[Robyt3]

1. Choose "Coordinate²" or a different preset that can show a warning.
2. Choose a too high target zone, so this warning is shown: "Your target zone seems too high for this c², try lowering it."
3. Switch to a different preset without this warnings, for example "Other c²".
   The warning will not disappear unless you reload the page.

Alternatively, keep pasting invalid text into the save import textbox to keep adding more "Your clipboard did not contain a valid Trimps save." errors.