I've been thinking about upgrading from a B to a B+, so I went and looked at the Raspbian Stretch with Desktop download I recently used to set up a new SD card for my Pi-Top running the Model B. It is in fact running the 2018-03-13 release. So if anyone is wondering if this version of Raspbian is Model B compatible, yes it is. I presume that means I could swap in a B+, as the OP tried to do, and it will run OK?
Any of you who are running a Pi-Top on the newer B+ model....I read it is supposed to have "improved thermal management". I had to add heat sinks and a small cooling fan to my Pi-Top when I got it, because it's Model B Pi kept crashing or freezing up until I did, especially trying to run any of the Pi-Top provided software such as CEED Universe. I am wondering if you folks with the B+ are running their Pi-Top without any cooling fan (are you using a heat sink?) and especially with the slider closed over the board? I have to leave the slider cover removed.
I measured the CPU temps before and after adding the fan, using an IR Thermometer gun with laser dot targeting, and if I recall correctly I lowered the temperature on the CPU heat sink by 20-30 degrees by cooling it. I can't say it never hangs anymore, but it does so far less often now. It would be nice if I could ditch the fan though, because it takes up precious real estate for any add-on boards. I had to use externally wired speakers because the Pi-Top speaker I bought has no room to mount with the fan in there.
Any comments are welcome. :)