Couple of points here:
- Unfortunately, movie (and batch) had a bug related to +s. Thanks for posting this - I have now submitted a pull request on Github that fixes it, so if you are able to build GMT from source once this is merged then I recommend that.
- I am not sure you have understood the purpose of this modifier. All it does is to change the numbering on the output products - it does not start later in the sequence for the input data. If you have 1300 files and you want to use a frame counter starting at 300 through 1300 to get the right names then you need
-T300/1300/1I think. The +s is mostly for breaking up gigantic renderings across multiple machines and hence there is the need to not start at frame 0 for all those separate jobs… So if I understand your correctly you should be unaffected by the but since you don’t need to use +s.