Consider two versions of What is the modulus of continuity of this function that is continuous, increasing and bounded but nowhere locally Hölder?. Notice that, in the first version, the linked question title does not expand; whereas, in the second version, it does:
My guess, which seems to be borne out by the experiment shown in these two screenshots, is that it is the ‘ö’ of ‘hölder’ in the URL that is the trouble.
See also my earlier question When are question titles auto-expanded? and @JohnOmielan's comment, linking
</s> are autocompleted on preview but not rendered when posted.