possible excerpt failure in WP 3.9

I just noticed on one of my sites that the whole post gets displayed after i upgraded to WP 3.9. Then i took a look on another upgraded site of mine that is a multisite. Same problem, even with unmodified twenty-fourteen theme and all plug-ins deactivated. After it seemed me that the autoexcerpt does not work, i tried to add a defined excerpt in the post editor. For me it seems even predefined excerpts will not get shown since updating to 3.9.

However if i activate a theme that has an own, inbuilt excerpt function then the excerpt will be shown in that theme.

I really find it strange. Can someone please check if the excerpts are functioning right or there must be some problem on my side? (however on 2 different domains then…)