SplitButton doesn't behave as split button using touch

Describe the bug

SplitButton doesn’t behave as split button using touch.

Steps to reproduce the bug

1. Create a split button with a default command and drop down (e.g. with content ‘Play’)
2. Try clicking the “button” part with the mouse => works
3. Try tapping the “button” part with touch => shows dropdown

Expected behavior

Since a default command is bound to the button, I don’t want to repeat myself inside the dropdown for touch (otherwise I would have used the DropDownButton). I would expect the SplitButton to be invoking the command when tapping the button part.

Screenshots

Using mouse:

Using touch:

Version Info

All windows versions (Windows 10 Mobile, and the 1809 update on a surface tablet)

NuGet package version:

<PackageReference Include="Microsoft.UI.Xaml">
  <Version>2.0.181018003.1</Version>
</PackageReference>

Windows 10 version:

• Insider Build (xxxxx)
• October 2018 Update (17763)
• April 2018 Update (17134)
• Fall Creators Update (16299)
• Creators Update (15063)
• Anniversary Update (14393)

Device form factor:

• Desktop
• Mobile
• Xbox
• Surface Hub
• IoT

Additional context

[GeertvanHorrik]

If it’s not working correctly as a button then that would be a bug. Please let us know how it’s misbehaving specifically.

Whenever you implement a command on the button itself (SplitButton.Command), then that will never be invokable. So you must repeat yourself in the flyout in order to actually allow the (most important) command to be executable.

I think it’s a UX design issue, that can be considered a bug in the apps using this button of the devs are not aware of this.

[GeertvanHorrik]

Then shouldn’t it be mentioned in the remarks of the docs? And I think it’s still a design issue, because in this case it’s not a split button at all (and I need to repeat myself in order to get the regular button behavior, it’s actually not working as intended on touch devices).