Now using 10.0.0.116 and have noticed this in a few files this morning.
But just had a "play" and come up with a very simple example:
Very simple text file:
What happens selecting a few words in this file, it doesn't highlight the 1st occurrence of the selected word, but does highlight the rest if you select the 1st one.
Selecting "this" and "that"
Selecting "is" produces a strange result, highlighting the "is" at the end of "this" at the end of the line:

But it's fine if there is more text after the last "this":
But the "and" seems to always work:
Obviously not a show-stopper but I've found this to be a really useful feature.