# Why do greek characters in math mode sometimes look tilted in OneNote 2016?

I noticed that MS OneNote 2016 displays greek characters differently, but I'm not sure when.
Above, the otherwise case is written as \delta(\vartheta_k - \vartheta _(k+1)).
Why is one of the two theta in cursive?

I have written this Q&A to share my own insights, but would be interested if you have more information.

Experimenting shows that it depends on how soon you type the underscore (_).
If you type \vartheta_k, the symbol will be in one style and if you type \vartheta _k (mind the space), the character will be tilted/cursive.
Interestingly enough, this seems not to happen to other characters. I'm unsure whether it's just the greek symbols, but for example the element symbol ∈ written with \in does not have this feature.