Redmine

I wonder why, but on one Redmine I manage, the Search box on the upright side is filled in with a text "Search". Nothing to care about except it does not get emptied when you click on it, so you have to manually delete the "Search" text before being able to enter your criteria and actually search.

Other Redmines I manage do not show this behaviour.

Any idea where I should look to fix this?

Thanks