Why do D.S. al Coda and Dal Segno with separate al Coda, work differently in Guitar Pro when al Coda is at the end of repeat? D.S. al Coda skips the last repeat.
There are still several questions here (though related enough that it counts as one).
- Is there a logical inconsistency in Guitar Pro's treatment of these repeats? Yes. If, after using the "Dal Segno" to go back to the beginning, it observed the repeat in m. 2, then it should also have observed the one in m. 4. If it didn't observe m. 4 it shouldn't have observed m. 2. This doesn't surprise me much; I haven't used Guitar Pro, but it seems to me to be rather under-featured as a notational tool. If you need to do a lot of writing I might turn to another piece of notation software.
- Should you observe repeats after a Da Capo or Dal Segno? This is a little bit trickier. The overwhelming convention is, no, you should not. If a D.S. or D.C. sent you back to an earlier section of music, you should ignore repeats (which you would have observed the first time you encountered them). This source helps explain (note, wherever it talks about "first endings," the same is true for simple repeats), and the topic has been covered here as well (don't let the OP's initial confusion confuse you). So the "bug" in GuitarPro would appear to be that it observed the m. 2 repeat after the Dal Segno.
The plot thickens because occasionally composers or conductors ask for exceptions to this rule. Context also matters; in the Minuet-Trio movement of a Mozart symphony, the "skip the repeats" rule is even more ironclad—unless some director has a pet theory or bit of evidence suggesting that in this one case it isn't. If the composer intends repeats to be observed, they had better communicate it in writing.
- Not asked, but a reasonable follow-up is: When writing music, how can I best make the repeats and sections clear to the performers? First of all, write out anything that's reasonably short without using any kind of directions. I understand that the example above is mocked up for demonstration purposes, but if the repeated material is only a few bars, it's better to simply write it twice than to make the reader jump backwards and forwards on the page. Even a simple D.C., D.S., Coda combination is deadly to sight-reading (and many worse mutations roam the wild). Performers are left hurriedly turning pages and scanning. In rehearsal, they make the impossible possible only by "decorating" the music with sticky notes, highlighters, and giant arrows (or perhaps colorful language).
If absolutely forced to use such directions (to navigate large sections), learn and follow standard conventions.