Video frames are not displayed directly as they're received. As frames tend to have dependencies on each other (cf. "I", "P" and "B" frames) it is often necessary to receive and keep in memory several frames before all can be decoded. Besides that, they also have a time code, as do the audio frames, to be able to synchronise them.
To cut a long story short, video frames are shown with "some" delay after being received. The delay is dependent on various things, some of them depend on the design of the settopbox (both hardware and software) and are not predictable.
If all of the streams are accompanied with a proper timestamp (video/audio/subs) enigma and the hardware take care they are presented to the user at exactly the right time. If the subtitles have no timestamps, enigma has no other choice then to display them when they arrive (or with a fixed delay).
The reason you see the subs disappear so quickly is that subtitles have no "end time". They are started and then "overwritten" by an empty subtitle. If the original and the "empty" subtitle happen to arrive at almost the same time, and have no time stamps, you'll have the effect you see.
It's not the way it's supposed to work, without timestamps.
Edited by Erik Slagter, 28 September 2013 - 16:43.