Hello mcseidel,

Thank you for posting in the community.

What I can suggest is enable the Activation behavior of WebHierarchicalDataGrid. To enable it, click the ellipsis (...) button for Behavior in the property window and check the Activation behavior in the Behaviors editor A cell is considered active when it is the current cell or the last to recieve an action, such a mouse click. The row or column to which an active cell belongs to is considered active as well.  The following are ways to activate WebHirarchicalDataGrid with the keyboard:

+/- Keys

Pressing the + key expands the currently active row if it has children and similarly pressing the - key collapse the active row.

Arrow Keys

• Move through the WebHierarchicalDataGrid cells.
• The arrow keys will let the end user navigate within cells only.
• With child levels expanded, navigation depends upon the arrow keys the end user is pressing. Navigates up to the last cell within child level and then back to the active parent cell that was last active.

Tab

• Move to the next cell in a row.
• If the last cell of a row is active, then pressing Tab activates the first cell of the next row, if one exists.
• If it is the last cell in the last row, move focus to the next control.
• With child levels expanded, moves from the expanded parent cell to the first cell within child band.

Enter Key

• Move to the cell below.
• If already in the last row, then stay there.
• With child levels expanded, moves from the expanded parent cell to the first cell within child band. If in the last cell within the child band, pressing enter moves to the corresponding parent cell that was last active.

Shift Enter Key

• Move to Cell Above.
• If already in the top most row, then stay there.
• With child levels expanded, moves to cell above the current cell. If in the first row of a child level activation moves up to the last cell of the expanded parent row.

Shift + Tab

• Move to the previous cell in a row.
• If it is the first cell in the first row, then move focus to the control, and then to the next control.
• If in the first cell of a row, then move to the last cell of the previous row, if one exists.
• With child levels expanded, and if in the first cell of a child row, activation moves to the last cell of the expanded parent row.

Shift + [Any Arrow Keys]

• Begin cell selection from the active cell and navigate depending on the arrow keys the end user is pressing.

Some further reference could be found at:

http://help.infragistics.com/NetAdvantage/ASPNET/2012.2/CLR4.0/?page=WebHierarchicalDataGrid_Activation.html

I hope this helps. Please let me know if you have any additional questions regarding this matter.