Duplicate zero-length lines in subtitles not being trapped

Some DVB streams are appearing here in Australia with subtitles having duplicate lines with zero duration, i.e the same timecode for start and end. Using Subtitle Edit I can see by comparing the subs in my source ts files with those in the resulting mkv files MKVToolnix very cleverly corrects many faults in subs but not this new one.

The effect is to make an unreadable, mis-timed, piled-up jumble of lines of text on-screen. Is the solution something that needs to be permanently programmed into the program code by you or is there a way for users to add filters? I can't see anything about this sort of problem in the help.

I have been able to repair subs with this new problem in Subtitle Edit and then mux the new srt files into my projects using MKVToolnix.

I'm happy to upload sample files.