You are absolutely right. In a normal situation when people are talking, sitting or standing, you say "They are talking." But if people are talking in an extraordinary situation, laying down, or hanging with their feet on a rope, than you need to mention the situation.
The correct translation of "they are talking" is "ze/zij praten". Another possibility is "ze/zij zijn aan het praten". As a Dutch native speaker I really fail to see how it can ever be translated as "ze liggen te praten". So i don't think you have missed anything. De "liggen" has no use here.
The use of "lopen" is similar to that of the Portuguese language: "andar" means "to walk" and this verb is used in daily conversation to construct the progressive present: "ele anda falando" meaning "he is talking" but not necessarily right now, actually for a continued period of time, like days or weeks. In Portuguese, you will never think that someone is "walking and talking" when that phrase is heard. Sorry for mixing another language in this thread, but I would like to show that the Dutch language is not alone in employing that verbal construction!
I see a lot of people confusing the verbs "lay" vs "lie" in English.
(This is limited to when "lay" means to place something and "lie" means to rest or recline horizontally.)
That seems to be causing some confusion in some of these responses.
It's nothing to be embarrassed about, as even Eric Clapton and Bob Dylan got this wrong in their iconic songs.
One important difference: "lay" requires an object. "Lie" doesn't.
It's the past tense of "lie" that causes most of the confusion, I think. This is one of those many times when English is awful.
This conjugation chart should help:
Present Tense - Past Tense - Past Participle
lie(s) - lay - lain
lay(s) - laid - laid
Here's a link to study with a prettier chart and more memory aids:
As most of us are here to learn Dutch, not English:
Onthoud: liggen is stilstand, leggen is beweging.
(Remember: "liggen" is resting, "leggen" is motion.)
According to this web site--and it could well be incorrect--the sentence is in the continuous present and means "They lie (are lying down) and talk": http://www.dutchgrammar.com/forum/viewtopic.php?t=446
DL seems to have shoe-horned an extra skill into a module which was primarily about 'te + infinitive'. From reading the comments I am beginning to understand the Dutch phraseology, but with nothing in the tips to forewarn me I was trying to acknowledge the staan/zitten/liggen and Duo slapped me down! Please add something to the tips section.
Almost, that would be 'hij zit over de televisie te praten'. This sentence in particular is not so common, but similar to 'hij zit / staat / loopt over het weer te praten' (He is talking about the weather).
To make it more confusing, one could say: 'Hij zit om televisie te kijken' (He sits in order to watch television)
Even more far fetched is 'Hij zit om over televisie te praten' (He sits in order to talk about television, not meaning the machine, but the programming)
Not to be confused with "Hij zit om over de televisie te praten' which could mean both 'He sits in order to talk about the television' or something meaning that he sits in order to be able to speak to someone else without the television being an obstruction.
I start rambling, sorry.