[UPDATE] The FindControls<T>(Control seed, ...) methods have been revised. Now it treats a seed parameter as an INamingContainer instance.
It checks if a seed is an INamingContainer instance or not. If it is, it starts searching from that seed, otherwise - from seed.NamingContainer. 
So, now it has the same logic as the native ASP.NET FindControl method, as well as the Ext.Net.Utilities's FindControl one.

If you use the FindControls<T>() method and a seed is not an INamingContainer, you might need to use the FindChildControls<T>() method instead.

[NEW] Added the FindChildControl<T>() and FindChildControls<T>() generic methods.

[NEW] Created the BREAKING_CHANGES.txt files with the breaking change regarding the FindControls<T>(Control seed, ...) methods.