indexterm tag splitting?

FM 2017 Release, all updates installed, DITA 1.3, Win7Pro Machine.

I have created <indexterm> tags using both the new marker dialog that appears when I add the tag to a document, and also through the Edit markers pod.

My MO is to create one tag that contains all of the relevant indexing information for that section, e.g. topic:subtopic;restated topic:sub;topic alone

When I close and reopen the file, I end up with (in the example above) three different <indexterm> tags with the different terms separated out, so <topic:subtopic><restated topic:sub>, etc.

I guess this isn't problematic (output seems OK) but I liked keeping things simple with the single tag, and I don't recall this behavior in previous versions of FM that I have used.

Has something changed? Is this expected/desired behavior? I have not changed the R/W rules or EDDs for index terms.