ToolTip ignores specified DateTime format specifier

Question

I'm struggling with a strange issue regarding ToolTips in WPF:

First, the code:

<TextBlock Text="{Binding SelectedItem.Approver.Timestamp, StringFormat='{}{0:g}'}"
           ToolTip="{Binding SelectedItem.Approver.Timestamp, StringFormat='{}{0:f}'}" />

As you can see, the "g format specifier" (e. g. 2016-12-24 23:42) is used for the timestamp's display and "f format specifier" (e. g. Saturday, 24. December 2016 23:42) for its ToolTip.

However, what I get is: 2016-12-24 23:42. In other words: the ToolTip shows exactly the same format as does the TextBlock.

It gets even weirder when switching the TextBlock to the "f format specifier", too: the ToolTip just stays in the format specified by the "g format specifier".

So, I've got two questions:
a) Why is that?
and
b) How to enforce my desired format?

Answer 1

I got it working.

<TextBlock Text="{Binding SelectedItem.Approver.Timestamp, StringFormat={}{0:g}}">
  <TextBlock.ToolTip>
    <ToolTip Content="{Binding SelectedItem.Approver.Timestamp}" ContentStringFormat="{}{0:f}" />
  </TextBlock.ToolTip>
</TextBlock>

As Tooltip can contain anything, we should use its ContentStringFormat.