Weird behavior when debugging ASP.NET Web application: cookie expires (1/1/0001 12:00AM) by itself on next breakpoint hit.

I'm working on ajaxified (Telerik AJAX Manager) ASP.NET application using Visual Studio 2010 (runs with admin privileges) and IIS 7.5. Basically, everything on the page is inside update panels. As for cookies I have custom encrypted "settings" cookie which is added to Response if it's not there on session start. Application runs smoothly, problem was arising when I started the debugging it:

Actions: 

no breakpoints set, F5 - application has started in debug mode, browser window loaded. I login to site, click on controls, all is fine. Next I set *any* breakpoint somewhere in code, break on it then let it continue running, but once I break again (immediately after first break) and check cookie: it has expired date 1/1/0001 12:00AM and no data in value property. I was storing current language there, which was used inside Page's InitializeCulture event and obviously exception was being raised. I spent several hours trying deleting browser cache, temporary ASP.NET files etc, nothing seemed to work.

Same application has been tested on exactly same environment on another PC and no problems with debugging there.

After all I've found the solution: visual studio generates for every solution additional .suo file where additional settings are stored, like UI state, breakpoints info, etc, so I deleted it and loaded project again, tried debugging - everything is ok now.