DSO138 single shot

Hi, please don't laugh, I KNOW this is a toy, but toys may work in the range of their specs and those specs may be fine for some problems.

So I got a DSO138 "oscilloscope" to bridge the time until I get a Rigol DO1000Z (with the next tax refund, I guess :)). I found it to work surprisingly well in AUTO and NORMAL mode and a good tool for it's price to do some easy debugging on power connections and that sort of stuff. (I would even keep using it sometimes because it is easier to carry than a normal oscilloscope).

Now it WOULD also be a good tool to look at transients from pulses through caps, like e.g. the Arduino reset pulse, but I cannot get the single shot mode to run properly: I connected both crocodile clips to ground first. I set the pink trigger arrow at about half the expected peak voltage, the mode to SING and trigger to rising flank. Then I connect the red clip to HIGH.

Expected: Device takes a single range, and I get the trigger somewhere in the center, or on the rightmost screen of the horizontal range, or whatever. Device shows HOLD.

Is: Dives starts running (stats change), but graph does not change. After some time, stats stop again. Graph does not change until here. Now, if I scroll horizontally, graph updates over the full range, but is HIGH over the whole range. I think the trigger makes it read for at least the storeable time and only then stops, such that a fast rise is invisible on the edge or beyond. If I press HOLD after the trigger kicks in, the graph still only updates after I scroll vertically, but the trigger event is captured. Of course, with very high time res, it is hard to press hold fast enough and it is quite tedious. also kind of defies the purpose of a single shot trigger. Is this normal behavior for the DSO138? Am I doing something wrong? Does my device act strange?