removing the optimizeCompilations="true" attribute from on the compilation element in our Web.Config file.

After upgrading to VS2013 we ran into this issue on a large webforms application that we develop. We solved it be removing the optimizeCompilations="true" attribute from on the compilation element in our Web.Config file.
I also tried VS2013 Update 1 and VS2013 Update 2 RC and neither of them resolve this issue.