datatable Dynamic Load bug

https://snippet.webix.com/2haz1jws

1. Using scrollbar and mouse, scroll quickly to the bottom, so the records in the middle could not be loaded.
2. Click on some row on the bottom of the table to select it
3. Navigate with arrow UP keyboard key

Dynamic loading algorithm loads only one row, one by each request.
PageUP key doesn’t work totally.

If you try to do this from top of the table dynamic loading works as expected.

Strange is that when[after snippet reload] being again on the bottom you will hit:

1. KeyUP key to load few rows
2. PageDown key
3. PageUP key
   then all starts to work normally - like expected

I can confirm the issue, thank you for reporting it!
Most probably, the fix will be included in the next 5.x release.