I don't see this as a JavaScript specific problem. A similar issue can occur in IIS, for example. The details would be more elaborate, but the core issue would

I don't see this as a JavaScript specific problem. A similar issue can occur in IIS, for example. The details would be more elaborate, but the core issue would remain the same. A variable shared across requests screws something up under load. Seen it happen. This is one of the reasons I like shared-nothing architecture where the only way to share or persist something is via explicit caching or database.