Bonjour Mitchell,
Yes, your stressing the difference in meaning between the two verbs is very worthwhile, and your example illustrates one of the problems very well. Take your second sentence by itself:
Pendant que j'étais assis, les gens n'arrêtaient pas de se lever. It's obvious what you mean in French.
But in the English translation, While I was sitting, people kept standing up, it's not, because it's not clear if you were already seated, or actively trying to sit down (j'essayais de m'asseoir). I vote for this necessarily being translated as, While I was seated, people kept standing up (if that is, indeed what you mean).
So, yes, I think the way être assise is commonly translated is confusing, not just in your example, but in the dictionary. In French, the meaning is clear according to the choice of verb, while it's (what seems to me to be) the loose translation that muddies things up like it is in English.
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It's worth noting though, that I think your translation of être assis is actually too strict. Doesn't it also apply to the situation where you've simply been assigned a seat , which is clearly passive voice? As in,
Tout ce que je sais, c'est que nous sommes assis à la grande table. (être assis)
(All I know is, we are seated at the big table.)
It's this passive usage that actually got me into this in the first place. My first question was in regard to, do the French typically use the passive voice (être assis) in this case? Or, might they opt for something like:
Tout ce que je sais, c'est que nous allons nous asseoir à la grande table. (s'asseoir)
(All I know is, we are going to sit at the big table.)
which is very likely in English.
Merci.
Robert