FYI, I found I had to fix some of my data. It looks like you are using Build 38 lengths for the chromosomes. Most of my data (from GEDmatch and from recent FamilyTreeDNA downloads) uses Build 37 start and end positions, but some of my older data from FamilyTreeDNA used Build 36, in which chromosome 19 (for example) was somewhat longer, and so I had a segment at the end of chromosome 19 that was hanging past the end of the underlying bar:
For that little segment on the right, the start and end positions in Build 36 are 61 to 63 million; in Build 37 they are 56 to 59 million. The length of chromosome 19 in Build 38 is only 58 million.
I am not attempting to convert my data to Build 38 (not sure how I would do it anyway; probably there is a tool somewhere?). But you might consider switching to Build 37 to avoid any minor discrepancies, if most users currently have their data in Build 37. Or possibly make it configurable, in case another build becomes more common in the future.
Regardless, users should determine which build(s) are represented in their match data and be careful to avoid mismatches when combining older and newer data, or data from different providers – not just within this gramplet, but with any tool they use. GEDmatch gives users a choice of viewing comparisons in Buld 36, 37, or 38. FamilyTreeDNA currently uses Build 37. I haven’t used any of the other providers and don’t know what they are currently showing.
For those who need it, here is a handy reference of chromosome lengths in the different builds (use the drop-down menu to switch build number).