I have been finding that when moving a site (SPWeb) to a different location in the site hierarchy of a site collection that the breadcrumb would often (not always) be incorrect once the site had been moved.
If you didn’t know, SiteMapProviders are cached in the SharePoint object cache. I’ll put the sporadic nature of the issue down to the natural refresh cycle of the object cache but honestly I’m not completely sure why it doesn’t go wrong all the time. The important bit is that there is way to ensure that the breadcrumb is refreshed correctly every time. For the sake of completeness, here is the SiteMapPath control with its SiteMapProvider property set to CurrentNavSiteMapProviderNoEncode from the custom master page (if you want to read more about this you could start here):
If you are suffering this issue I suspect that mentioning the object cache was enough to put you on the right path but I’ll spell it out just in case.
If you run a few lines of code in a WebMoved event receiver (I blogged briefly about attaching these here) you force the object cache to be refreshed whenever a site is relocated. Be warned that if you have a site that leverages the object cache (e.g. use of the cross-list query object, or the content query web part which utilises it) that these operations will need to re-cache and may have some performance impact.
SiteCacheSettingsWriter writer=new SiteCacheSettingsWriter(site);
You may need to fetch the SPSite object that is passed into the constructor from within an elevated privileges block to ensure the current user is allowed to perform this action. Obviously that depends on expected audience for this action.