This sounds very inconvenient:
The page I am editing jumps to the top every time I press Backspace, making it inconvenient, especially for very long pages.
Since this is probably browser-specific, here's the user agent information:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E; InfoPath.2; rv:11.0) like Gecko
This is IE11 on a Windows 7 Media Centre PC? Interesting. We had a bug like this before but ISTR we marked it as fixed.
There was T141039, which seems similar. If it's related, it'll probably be because the page they're editing has a really long paragraph, and it'll be scrolling to the top of that paragraph at the start of the page. If it's literally going to the top of the window, not the top of the editing surface, it's likely something different.
Unfortunately closing this Phabricator task as no further information has been provided, and as similar T141039 has been resolved.
@Whatamidoing-WMF: After you have provided the information asked for and if this still happens, please set the status of this task back to "Open" via the Add Action... → Change Status dropdown. Thanks!