Comment # 22 on bug 1215987 from Felix Miata

SDDM v0.2 (as would GDM, conscripting any or all of ttys 1-3) conflicts with
workflow here, so I've been slowly getting it purged it from all installations,
which is how I found this problem. I wasn't able to find any way to get SDDM
back up on tty7+, so by now I have maybe about 2 or 3 left among Slowrolls and
TWs I will try when I can identify which.

Most of those purged got KDM3, TDM or LightDM as a replacement. I haven't had
any of them fail to launch startplasma-x11.