In tablet mode, OSK is not displayed in the WiFi network auth dialog

Test Case:
1. On a 2 in 1 laptop, use it in table mode
2. Start the installer and proceed to the WiFi step
3. Connect to an authenticated network
4. Type the password and authenticate

Actual result
The OSK is not displayed and the user cannot enter his password

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 4.18.0-8.9-generic 4.18.7
Uname: Linux 4.18.0-8-generic x86_64
ApportVersion: 2.20.10-0ubuntu11
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Oct 11 15:10:11 2018
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd quiet splash --- maybe-ubiquity
InstallationDate: Installed on 2018-10-11 (0 days ago)
InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Beta amd64 (20181011)
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)