If one types a dot after a symbol, content assist window is activated (cursor is the |):

val xs = List(1, 2, 3)
xs.|

If one types a space instead of a dot, the same window is activated, too, but with wrong members (see screenshot). Before, one has to activate content assist on typing a space by put it in Preferences > Java > Editor > Content Assist > Auto activation triggers for Java. Disadvantage of this approach is that content assist is opened every time one types a space and not only if the current expression is in operator notation.

Therefore scala-ide should has its own auto activation triggers which are activated only if it is necessary.