Lecture 2 of plutus-pioneer-program, introduces unstableMakeIsData
In the lecture it is advised to use the Stable version in production.
Lars explains that the Unstable version does not make any guarantee that different constructor numbers will be preserved for future versions of Plutus. He further adds that:
A newer version of plutus does it in a different way it would be incompatible and you would have round trip problems (??)
I understand the incompatibility issue, sure, but what exactly is a round trip problem in this context?