[Timbuktu 18.04]miscellanea/chvt didn't change to a text console

Image: pc-timbuktu-bionic-amd64-m3-20180412-29
Platforms: Storm3-1,Tata2AMD-2,Windu2-1

Steps:
1. Install pc-timbuktu-bionic-amd64-m3-20180412-29 image.
2. Use boxer to install sutton provider.
3. Execute checkbox by "sutton-cli"
4. Run miscellanea/chvt case.

u@u-ThinkPad-T480:/usr/share/plainbox-provider-checkbox/data$ checkbox-cli -v
INFO:plainbox.config:Loading configuration from ['/etc/xdg/plainbox.conf', '/home/u/.config/plainbox.conf']
INFO:plainbox.secure.providers.v1:Provider initialized com.canonical.ce:oem, version 1.0
INFO:plainbox.secure.providers.v1:Provider initialized certification-client, version 0.33.0
INFO:plainbox.secure.providers.v1:Provider initialized plainbox-provider-checkbox, version 0.43.0
INFO:plainbox.secure.providers.v1:Provider initialized plainbox-provider-resource-generic, version 0.36.0
INFO:plainbox.secure.providers.v1:Provider initialized plainbox-provider-tpm2, version 1.7.0
INFO:plainbox.secure.providers.v1:Provider initialized com.canonical.plainbox:manifest, version 1.0
INFO:plainbox.secure.providers.v1:Provider initialized com.canonical.plainbox:exporters, version 1.0
INFO:plainbox.secure.providers.v1:Provider initialized com.canonical.plainbox:categories, version 1.0

Expected results:
Screen change temporarily to a text console and then switch back to your current session.

Actual results:
System keeping in current session,didn't change to text console.