Well, I know that the properly made subs shouldn't have overlapping timings, but in reality some have (usually for TV series) and most players (including pure kodi) manages to display them just fine, so players not having problems with showing them is the standard.
In this case, the subs aren't literally overlapping - simply ending and starting next the same milisecond, more like touching than overlapping.
Even the media player built into my TV manages to show those subs, so I suppose the way to fix it is simple for developers (simple as auto delaying overlapping subs by 1ms) and it would be cool if the native himedia player wouldn't struggle in such cases.
It's not one of those "fix something you failed to do properly", but one of the "add this to make the player better in real life, imperfect usage".
BTW
It's not Kodi problem (it works fine), just the himedia's media center and Kodi with himedia's wrapper.