[woodcote]

I've not used the Carrera 1/24 scale high banks, but having used other high-banked turned (especially rigid plastic, like Carrera), I've found mixing flat pieces in a banked section can be problematic. The banks are pretty much designed to be 180-degrees with the entry and exit straights gradually lifting up from flat to meet the banking. If you have two 90-degree curved sections linked by a straight, then I don't think that middle straight is ever going to work as you want it to. You probably can tweak the section (maybe try and bend it a little), adjust the banking and that might give you a compromise that works and at least gives you two parallel straights.

As for the digital / analogue hybrid powerbase lanes being connected... it will either be something you haven't snipped in the powerbase or it will be any power taps / jumpers you have are connecting the two lanes - not a problem in digital, but it will cause this issue in analogue. Carrera lane changers and pit lanes don't cross the power on the lanes, so they won't be causing it.