Group blend = layer blend ?

Question

I have a very strange case, which I think is theoretically impossible ... (headscratching):
I have "group1" and inside that group, only one layer: "layer1". The blending mode for "group1" is vivid light and for "layer1" it's "normal".
Now, if I change "group1" to "pass through" and "layer1" to "vivid light" ... the result is completely different, while it should be the same, shouldn't it?
How is that possible ?!?

Answer 1

Ok, sorry for misinterpreting you then, I thought that was what you meant when saying: "layer groups when you apply a blend mode to them take their VISIBLE contents and apply the mode to the whole area, so its similar to applying a neutral 50% grey behind transparent pixels."
So if that's not what you meant, than I'm basically back at square one and don't know at all,
HOW you explain what accounts for the different blending results of a layer vs. of a group.
All livedocs has to say on this is:
" By default, the blending mode of a layer group is Pass Through, which means that the group has no blending properties of its own. When you choose a different blending mode for a group, you effectively change the order in which the image components are put together. All of the layers in the group are put together first.
The composite group is then treated as a single image and blended with the rest of the image using the selected blending mode. Thus, if you choose a blending mode other than Pass Through for the group, none of the adjustment layers or layer blending modes inside the group will apply to layers outside the group."
I couldn't find any other "official" definitions of the way groups affect blending.
According to this definition, all that a group actually changes is the interaction
between more than one layer inside a group.("...is then treated as a single image..."). So basically, for a single layer, there shouldn't be any difference at all between my two screenshots above. They should blend the same. A different result is against livedoc's definition.
What I meant with my last paragraph is that the "blend layer" used in my example above contains no (or almost no) 100% opaque pixels. So it's a particular case and thus maybe not the best starting point for evaluating basic rules. That's why I suggested to just use a white text layer instead (which has 100% opaque pixels).
Try the same thing as above: Cycle through all the blending modes for the layer. Then put the layer inside a group and cycle through the group's blending modes. You'll see, the results are not the same, and again, that's against the abovementioned definition.
There must be other rules in play as well here. I did an extensive Internet search, but couldn't find any other rules, that would explain the results.