ng-options with "track by" in select box makes all clicked options "selected"

[mjmlopes]

I'm submitting a ...

• regression from 1.7.0
• security issue
• issue caused by a new browser version
• other

Current behavior:
By visiting this page https://code.angularjs.org/1.7.8/docs/api/ng/directive/select, section "Using select with ngOptions and setting a default value", all of "Make a choice" options which are clicked on will have the selected="selected" parameter set:
<select name="mySelect" id="mySelect" ng-options="option.name for option in data.availableOptions track by option.id" ng-model="data.selectedOption" class="ng-valid ng-not-empty ng-touched ng-dirty ng-valid-parse"><option label="Option A" value="1" selected="selected">Option A</option><option label="Option B" value="2" selected="selected">Option B</option><option label="Option C" value="3" selected="selected">Option C</option></select>

Expected / new behavior:
Instead of
<option label="Option C" value="3" selected="selected">Option C</option>
could be selected only:
<option label="Option C" value="3" selected>Option C</option>
, and only for the current option which is selected, removing the parameter for the other not selected options.

Minimal reproduction of the problem with instructions:
By visiting this page https://code.angularjs.org/1.7.8/docs/api/ng/directive/select, section "Using select with ngOptions and setting a default value" and the default option is "Option C". When clicking on other options, to the respective option tags will be added the parameter selected="selected".

AngularJS version:
1.7.8

Browser:
Chrome 78.0.3904.97 (64 bit)
Firefox 68.2.0esr (64-bit)
(both running in Debian 9)

[Narretz]

While this isn't ideal, multiple selected attributes don't actually interfere with the functionality of the select, e.g. the right option should still be selected and in the model. Ofc it's possible that accessibility tools use the selected attribute, and it makes writing tests that check for selected more problematic.