Like with the other report this isn't a bug report. It is a symptom of difficulty in explaining how all these complex features interact with each other and thus users having the wrong expectations.
Compare the plans for a circa v13 execution and a circa v14 execution to see what was gained.
In short, expecting even a custom plan of a prepared statement to match an unprepared statement is incorrect. There is still considerable saved worked done without knowledge of parameters that has to be ignored, not discarded.
