This week I had a joy of spending several hours trying to solve and intermitently happening bug. In short, some 2 times out of 3 the YUI selector utility failed to lookup elements in an XHR loaded HTML fragment. After digging quite deep into the YUI code, I found that it was actually the fault of the way ASP.NET MVC treats partial views.

Summary

• ASP.NET MVC allows use of ASCX as “partial views”
• It correctly assumes, that uniqueness of ClientID should be preserved
• It incorrectly does not prepend an alpha-character to automatically generated GUID based IDs
• User agents and selector libraries may correctly ignore such invalid IDs
• Solution: override ViewUserControl.UniqueID

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