Managing cross-thread communication on issue/bug reports

Question

On my current project we have two or three engineers who are tagged as Tier 2 or Tier 3 support. We often work directly with customers to gather detailed information about bug and issue reports.

Frequently we get cross-talk in the email threads and conversations about issues. While discussing Issue #1, someone pipes up "Oh by the way we found Issue #2". Or having resolved Issue #1 we get asked "Thanks for fixing that. Where are you with Issue #3".

I find this incredibly annoying and it can make it tricky to unravel threads when reviewing the history of a bug report because the threads are all mixed up.

Can anyone suggest any strategies to manage this communication? Is there a polite way to address this and keep things single task focused? Is there a disadvantage to a single issue focus?