arrows from different stems in same direction are not marked as distinct

The arrows drawn under a structure like:

(((((...)))..)))

should be distinct for each contiguous helical segment - e.g.
-->--> <-- <--

However, the rendering code inherited from version 2.5.1_rna only uses the adjacent annotation elements to decide helical continuity - not the helical numbering assigned using the RNA structure processing algorithm used to generate the alignment's helical colourscheme. This means, the arrows can only be rendered as:
------> <-- <--