thanks for the replies.
If I remove the clock the dot disappears - if I re add the clock it reappears.
My widgets are usually locked but when the issue shows up again I’ll try unlocking the widgets to see if it makes a difference.
I went off to work this morning and let the computer go into standby on battery. When I came back a few hours ago and powered back up it hasn’t as yet reappeared.
I’ll keep an eye on it and see what happens but it had until now persisted over multiple reboots.
To me it looks normaly as the point to click on to let it explode in the hidden applets/icons (like device notifier, Kwallet if running and a few others). And it says something like that when I hover over it.
In my desktop (KDE 4.11.5) it is white with a thin grey border, but other icons there, like Klipper and Volume, look a bit different also. I guess they call that a different “theme”.