One of the many places where using strings instead of char arrays will trip you up. I haven't searched for one, but I've never yet seen a situation where strings solved a problem in such a simple and elegant way that it warrants rewriting half of Matlab for.
I'd suggest looking if there is already a bug report (and create it if there isn't). They will either solve it in an update to R2018b, or in a later release. Until then, just use char arrays. I'm also still using get and set instead of dot-indexing, because I generally don't need to go multiple levels deep (which is the only situation where dot-indexing is better). Fun fact: in set and get the properties are not case sensitive, while with dot-indexing they are.
