I have a Iguana v6.1.0 global dashboard instance and I have found the search term does not reapply when returning to the global dashboard.
1) From the global dashboard, search for a channel then click into it.
2) Follow the breadcrumb back to the global dashboard
3) The global dashboard’s search term is still present, but not applied
—> can re-apply manually by editing then hitting enter
Full disclosure: the global dashboard is v6.1.0, but the monitored instances are v.5.6.20