Well I never use the panel as it just seems to get in the way.
But I tried your repro and can't confirm as actually the panel remains open when a project is closed and re-opened.
If you actually quit Cubase it will be lost....but it takes one click to re-open and you only need to do it once on opening Cubase, so is hardly an issue.
EDIT...sorry slightly misread your post....my panel always opens in the same position once I have positioned where I want it.
i7 email@example.com, 12Gb, W7HP x64, Cubase 8.0 Pro & 7.5.30 x64, Audient iD22, Alphatrack, Wavelab Elements 7.2.1.