Why does my trace reference 'pulse'?

[Arcadia]

I've been having an on-off issue that when the trace reference is turned on and I hold the cursor over an item to select it the whole screen 'pulses' or flashes as if its repeatedly rebuilding or something and the zoom and pan is erratic. Happened in v12 too and I've just put up with it and used trace as little as possible. In the latest case the trace was a simple 2D line drawing.

[vistasp]

Have a look at this page in the Wiki.

[Arcadia]

Thanks but I have read this before and it is no help. My problem is not described there. And as I mentioned it happens even when the trace is a simple 2D line drawing with no rebuilding required.