EDIT 2023: The correct behaviour is obtained if the line operator is used. Objective of bug fix: Restore this behaviour but without use of line operator.
Due to API changes, Assign() is partially broken. It just evaluates it's arguments but is not evaluated itself.
An option might be to integrate the replacement into the pre-processing. This also might work for Solve() (integrate the Maxima function call into preprocessing)!
But maybe, the preprocessing isn't under control of the plugin...
