Theme installed success message not showing when installing multiple themes

[anilhada]

How to get bug:-

First go on Appearance - > Theme -> add new

1. Click on uninstall theme Preview button. after that preview page will open.
2. Click on install button and same time click on next button near by install button.
3. Next theme preview page open again click on install button and click on close button.

In this case we are install two theme but install massage will appear on only one theme.

[joyously]

Is this scenario a little fishy? I'm not sure how that theme preview overlay is coded, but by navigating away from the page of the theme that is installing, the javascript handling the messages from the server could have been replaced, so how would it receive or display the message?
(I'm surprised the test case didn't go further, and show that there was an error when clicking on the Install button for the theme that didn't get the "successfully installed" message.)

So does the fix involve moving the javascript into the Theme page instead of in the overlay?
Or is it more like "Don't do that"?

[poena]

Compared to plugins, I don't believe that installing two themes at once is supported.
Perhaps the next and previous buttons need to be disabled while the first theme is being installed.