I hope the issue is with Page scroll bar. I tried the similar scenario on my end and the page seems to maintain its scroll position while expanding the PanelBarItem. But i was able to replicate this issue when a postback occurs on expanding the panelbarItem. I resolved this issue by setting the following Page attribute.
I understand where you coming from but mine case , it cant be applied as i dont a\have a aspx page as i am doing it in a web part in sharepoint . I only have the .VB file as my aspx page only generate when sharepoint run and it create my page Aka web part .