Created attachment 108589 [details] demonstration plasma 5.11.2 on Arch. The same tooltip has correct width when I move the cursor from right to left instead. My gif shows the issue.
it affects plasma 5.12 beta on Arch Linux.
There seems to be something funky going on when a tooltip does not have a sub text. I can also reproduce when moving from Printer (which has "queue empty" subtext) to device notifier which just says "no devices"
Git commit f31e7860d98f3c66888f1102a7cf3c47f31e2a59 by Kai Uwe Broulik. Committed on 26/01/2018 at 14:49. Pushed by broulik into branch 'master'. [Default Tooltip] Fix sizing Unset the Label's default height which completely confuses the renderer either shifting the item vertically (e.g. when toggling system tray popup), or letting it get too wide (e.g. when moving from a two-line tooltip to a one-line tooltip). Also let the Layouts figure out sizing rather than trying to overrule it with flaky values. Related: bug 389371 Differential Revision: https://phabricator.kde.org/D10077 M +6 -6 src/declarativeimports/core/private/DefaultToolTip.qml https://commits.kde.org/plasma-framework/f31e7860d98f3c66888f1102a7cf3c47f31e2a59