You don't get this (initial) behaviour, though. Not on any 'scope I have worked with. What you get is the post-menu triggering behaviour.
I certainly get this behavior on my DS1054Z, and consider it to be perfectly normal and expected. And this guy gets it on his DS4024 (but has not understood it either)
Thanks for posting that. Note that the video seems to show a
consistent behaviour, with no change occurring. Whatever algorithm is being run to calculate the trigger point stays the same. This didn't appear to be the case with the Siglent -- but maybe it is just being modified in some way.
After more fiddling, it appears that you
can (with patience) get back to the first type of behaviour. Sometimes. Unless I was hallucinating, because now I can't get it to do that again.
This initial result (Auto trigger mode, but that doesn't matter)...
...is not the same as this second result (obtained by simply opening the trigger [Type] menu -- not changing it):
No
change to any settings was made, but the 'scope seems to re-evaluate the calculation -- either the algorithm gets re-started or some other process is involved.
Secondary point, not related to this bug (which is more of a weird aberration, as you can get back to that first behaviour with some effort) -- I consider the second screen-grab above, to be 'correct'. The only way it could find a genuine trigger point would be if the algorithm found something that looked like a trigger. If you look at the first screen-grab you can see that rectangle where no data points are present to the right of the central graticule (the trigger point). That is an artefact of some kind. It is persistent, and anomalous.
You should set the dot mode of your Rigol and see if you get the same artefact -- that rectangle of exclusion. If so, the same algorithm must be in play.
Why the action of opening the trigger [Type] menu might restart the algorithm is explicable by the code restarting (interpreting it as 'restart the calculation with this trigger type') -- but the result changes, so some recalculation must be occurring.
Whether this has any practical effect when triggering on real signals, I don't know. My second possible bug issue (with the pulse with an embedded 'glitch') seems to be a triggering issue, and has a similar 'solve by doing nothing (except opening the menu)' solution or work-around.
Consistent, predictable, behaviour? Too boring, I guess. (I bet the code running on this 'scope looks... interesting...
)
Well:
If I have nothing better to do sometime I may try to figure out what is going on here, but for now the underlying logic (?) eludes me. I'm still calling this a bug.