Colin Kraay did study such overstrucked coin, and provide a perfect theory.
The mint was working like this.
3 workers, 1 put the coin on the overse die, and the 2 others had reverse dies and hammer for stricking. so if the second guy was stricking too quick, the coin wasn't out of the die and was strucked a second time. there is no real willing, it's only a mistake of stricking.
Such mistakes have a great interest, for example, my sestertius provide us the evidence than the "final issue" of the RIC don't exist, the coin with P M TR P VII COS II P P was strucked simultaneous with the coin with short titulature.
Your coin provide us the evidence than there is 2 phases in the last issue
The 2 coins together tell us than 1st phase was long titulature (like MARTEM PROPVGNATOREM) and second phase with short titulature (like MARS PROPVGNAT)