Case 82 and Case 129

Put both of them in a pot and stir. 

Am I reading the two cases correctly?  Case 82 says you can finish from either side (because the windward mark is no longer a mark of the course but it is now a finishing mark) and case 129 says you have to finish from the right, leaving the mark to your port side, while to the definition of "finish" which usually places the finishing boat to the right and the finishing mark to the left.
Can somebody clarify?

John and Henry .. hmm .. that's not how I look at Case 129.

Let's take Case 129 first as it's more straightforward.  It basically restates the definition of finish .. in that a boat finishes when it crosses the finish-line from the course-side.  Once a rounding mark gets converted to a finishing-mark, it is the line definition and the course-side determination that takes precedence (and the original rounding designation no longer is relevant). 

The course side is determined by the rhumb-line from the previous mark to the finish-line.  The side of the line the rhumb-line intersects is the "course side".

Case 129's image shows it simply.  Though the mark was previously a port-rounding, to cross the newly formed finish-line from the course-side, boats must *leave the mark to starboard when they cross the line.

(*Note that they actually do not need to "pass" or "round" the mark.  A boat finishes when her hull crosses the line .. and by def: finish .. she need not cross the line completely .. that's why I used the word "leave").

Now Case 82 basically says that anytime a finish-line is laid such that is it difficult to determine which side is actually the course side, boats may cross the line from either side to finish.

In the OP .. assuming the previous mark was off the bottom of the picture, the rhumb-line from the previous mark was actually parallel to the finish-line (and thus doesn't actually intersect the finish-line on either side).  Therefore, Case 82 says that boats can finish by crossing from either side.

This is why ROs are trained to put the S Flag end of the finish line in a place that makes the course side unambiguous, i.e. where the finish line will be perpendicular to the course from the previous mark.  Moreover, they're strongly advised to place the S Flag so that competitors can cross the line to on the same side of the original mark as they would have passed it as they rounded.  

The scenario above is the result of an error (a la baseball, not evil).  As the marksetter has laid the finish mark, they finish either way, on whatever tack they want since there is no obvious preference.  It would be legal but inelegant;  I wouldn't want to be dealing with redress on the issue, because local judges can be special. 

 A properly laid finish line would have the mark boat displaying the S flag set to starboard of the the mark, looking up the course, at a point that put the finish line between the mark boat and the mark at right angles to the course from the previous mark.

 The course was shortened and signaled just like it says in the OP. So—what should the RC or Jury do in this case?

It doesn't matter which side of the mark boat the S flag is displayed on - the entire boat is a mark, and the position of the flag on the boat isn't clarifying.  In practice, the finish crew (probably the marksetters) will put the flag on their boat wherever they can attach it, with preference given to a spot from which they can sight the line.  

I feel that judges and race officers should do a bit of cross-training, so that everyone knows the rule issues and the practical ones.