Partial doesn't trigger soft select in override completion

[333fred]

Version Used: a51b65c86bb0f42a79c47798c10ad75d5c343f92

Steps to Reproduce:

class Base
{
    public virtual void M() {}
}

class Derived : Base
{
    public override $$
}

At the $$, type partial and hit space.

Expected Behavior:

partial is left alone. I would also expect partial to be shown in the completion window, but afaict no keywords are shown in the completion window here. A fix here will also affect required, as that suffers from the same problem.

Actual Behavior:

partial is replaced by whatever is selected in the completion window.