Cannot scroll rows when mouse pointer is over freezing columns

Steps to reproduce

1. run zssapp
2. freeze 3 columns
3. move the mouse pointer over freeze columns like
   
4. scroll rows

actual result

cannot scroll to rows below.

if you move the mouse pointer over non-frozen columns (after column D) and scroll, you can scroll rows.

Debug information

In Excel, users can scroll down rows no matter where the mouse pointer is.