Moved as a separate issue from https://github.com/backdrop/backdrop-issues/issues/1399#issuecomment-201...
...which also brings me to the "more details" dialog:

Again here, it should change to "1 installation" because people might confuse it with an action the way it is now.
I also thing that we should be more verbose (like "x reported installations") and perhaps add download count in last week/month. Then we should move that info in a second line below the "last updated" line.
To the right (where the reported installation is currently), we should add a "Add to installation queue" button. People now have to close the dialog and make a second click in order to do that. This is also prone to error because they might click on another "Add to installation queue" link in the list after they have closed the dialog.
The dialog title should change to "Module/Theme/Layout details" or "Project details".
Here's a mockup of what I'm proposing:

Recent comments
Thanks, the /tmp folder was the problem. I moved it elsewhere and then the updated worked. Thanks again!
Update 1.35.1 appears to install but hasn't
Probably not the reason, but worth to do a quick check: Sometimes the update cache interferes, so if something's odd with updates - some module (or core) claims to have updated, but then...
Update 1.35.1 appears to install but hasn't
Nope, not touched any permissions!
Update 1.35.1 appears to install but hasn't