This has been bugging me for ages in the extension manager updater. Hopefully this might help others fed up with the problem.
Affected all of my sites originally migrated using jupgrade!
This is the solution :
plus.google.com/106742096640193690159/posts/41NytcWkokX
Just throwing this out for anyone who may be having problems with the one-click update for sites that were migrated from 1.5.23 to 1.7.x using JUpgrade. File comparison showed different versions of /administrator/components/com_installer/models/update.php (lines 180-181) on my site vs. the file found in both 1.7.0 and 1.7.1 full packages (even though the build id was the same?).
After uploading the version from the full package, the one-click update worked fine.