I found a strange bug in GWT Material DatePicker, it works on officiat GWT website too:
If you go here - https://gwtmaterialdesign.github.io/gwt-material-demo/#pickers , try to pick some date, close DatePicker and open a new tab in your browser and go back, DatePicker will be opened. So, how can i fix this?
Yeah it's a bug. Hope they'll fix it someday.