Yes Deano, the same is happening with me; using the Opera browser.
I've been very quiet over the past few months due to health and other problems but I don't recall having issues with Page Builder. I do have these issues and others with Menu Builder, which on a large site it's almost impossible to drag anything anywhere.
I wanted to verify this issue with other people before i change it.
Is anyone else having a problem dragging blocks around in the page builder? Example, the drag helper appears way off to the left of where the mouse cursor actually is.