Hello,
I've seen it in the WPF report viewer, that I'm using, perhaps the problem is also in other report viewers.
When the report viewer is loading the report, the number of pages is increasing until the report is fully loaded. If I change the page number before the report is fully loaded, the displayed page is reset to 1 when the report is fully loaded!
To view the problem, you need to have a big report that takes enough time to load, so you can change the displayed page before it is fully loaded.
Regards