Am 27.09.2016 um 11:15 schrieb Sven Van Caekenberghe <sven@stfx.eu>:

PS2: Another really annoying problem is the following: he saved all his (really important) scripts using Script Manager as a FUEL. Moving between 4.0 and 5.0 FUEL stops working (version incompatibility) - this is really not cool, why would a newer FUEL not be able to read older FUEL. He ended up copying string data by opening the binary FUEL file in a text editor.

it is like that from the beginning. I guess there was the fear keeping everything compatible would be a huge amount of work. But it is indeed an annoying thing. The usual way to deal with it is open pharo4 and materialize the fuel file then upgrade fuel to the version pharo5 uses and save again.