Steps to reproduce: 

1) Find any firing alert in the chromium.perf tree
2) Click on "File Bug"
3) Click on the "Select priority" dropdown
4) Select a priority

EXPECTED: The priority you chose is selected and the dropdown goes away.

ACTUAL: The dropdown remains open, blocking your view of other dialog fields (like Label). Furthermore, if you click on the same dropdown item again (thinking you may not have clicked the first time, for example), the dialog closes altogether. If you click the "File bug" button again to reopen the dialog, the problem persists.