KDE - can you "add widgets" to Panels?

[rickst29]

Hi. I'm running Cauldron (Beta 2, plus all nightly updates). But I've also got a big pile of 4.8.x KDE libraries, built from source. (As in, I've just written a couple of fixes and NEEDED to test them. My kde-wokspace libs, the ones which include plasma, are fresh from KDE Git -- yesterday.)

I had the "two default panels" issue, and deleted the old one (the one which didn't contain 3 dots to "show Activities".
After this, when I try to add widgets, I get a a grey panel -- without any widgets or text inside, and no searchbar, and etc. (Nothing but a gray rectangle.)

Does anyone else have this issue?
I have a couple of ways to pursue on my own, but I'm curious whether you other Cauldron users have it too. (If so, then it's Mageia-related. If not, then it's strictly a "Newby KDE-Developer with quick-typing fingers, really slow Brain-related.)