add a coment referencing issue #621

index.bs

@@ -1484,6 +1484,13 @@ steps:
         <var>uuidExclusionFilters</var>.
 1. Let |browsingContext| be [=this=]'s [=relevant global object=]'s [=browsing context=].
 1. Let |promptId| be a new unique opaque string.
+
+Issue: In practice, the device list is dynamically updated while a
+prompt is open. The spec text currently does not reflect that but this
+event might be emitted multiple times with the same `prompt` ID and the
+fresh device list. See
+https://github.com/WebBluetoothCG/web-bluetooth/issues/621.
+
 1. [=Trigger a prompt updated event=] given |browsingContext|, |promptId|, and |scanResult|.
 1. <p id="requestDevice-prompt">Even if <var>scanResult</var> is empty,
     <a>prompt the user to choose</a> one of the devices in |scanResult|,