Scrollbar scrolls unexpectedly when column width is changed. Check the following video for a reference:
http://screencast.com/t/Y6IwtREc

Implement a way to group columns cells vertically.

Just run the attached project and scroll horizontally to the very end several times (at least two times).
I tried disabling the column virtualization but this did not help.

This issue will be resolved with Q2 2015. 
A new virtualization mechanism for ColumnGroups will be introduced with Q2 2015. A property EnableColumnGroupsVirtualization is exposed with default value True for enabled virtualization. Setting it to False will enable the old logic. 

Columns with * width are not measured correctly when GridView is placed in ScrollViewer and its width is changed.

Added the CanUserSearchInHiddenColumns property which indicates whether users can search for content in hidden columns. The property is available with our 2017.3.1127 internal build.

The RowStyleSelector is great for dynamically styling rows, but there doesn't seem to be an easy way to dynamically apply a style to selected rows - they just take on the default style. Something like a SelectedRowStyleSelector would be a great way to dynamically style selected rows. Thanks!

The group panel item image of a column with custom header is blurred

Border is not correct when FilterRow is on and Column header is wrapped. Sample and Screenshot attached.

Sample:
<telerik:RadGridView ShowSearchPanel="true" ShowSearchPanelCloseButton="false"
or
<telerik:RadGridView ShowSearchPanel="true" ShowSearchPanelCloseButton="Hidden"

There are cells exported for the group rows, but they are empty. If you define ColumnGroupDescriptors instead GroupDescriptors, then the exported data is the correct one.

this is not related only to grid-inside-grid scenario (HierarchyChildTemplate), but also for a flat (classic) grid control. If you have a GridView and any other control (ex TextBox), you will notice that if you move focus from GridViewCell to TextBox, both

When you define a style targeted at GridViewCell with a color without transparency, horizontal grid lines are hidden.

When two columns in two separate column groups have the same name and they belong two separate column groups, the column group names of the parent column groups can be appended to the display content of the GridViewGroupPanelCells.

For example, the duplicate Code columns in the attached image should have content "PG Code" and "VENUE Code" respectively.