I discovered this issue when trying to resize a RadDock that was in a horizontal dock with a width of 600px. The dock was only 200px but I could not increase its width to 600px.

The culprit is in the way the available width of the horizontal dock is calculated. The function caluclateZoneFreeSpace in the dock object ignores the height of the dockzone and whether or not there are docks on multiple rows.

A resolution to this would be to return the remaining width available on the current row ignoring all other docks except the current dock. Additionally, if the dockzone is sized statically, it might be beneficial to determine if resizing a dock horizontally would cause a dock to reposition on another row, potentially exceeding the dockzone height.

A workaround that works for me can be found here:

http://www.telerik.com/community/forums/aspnet-ajax/docking/resize-dock-issue.aspx#2604861