Well, it's interesting, maybe the charger (USB to wall) is defective.
Or still caused by the chosen % range ... in that upper part of percentage range the Li-Ion cells draw only a part of its max allowed amperage.
To find out about this oddity you'd install a battery app for measuring the charging amperage like 'Battery Monitor Widget'.
The app logs the charging and will show you amperage and %-capacity, even in a graph, no need to monitor it by yourself.
So you'd log a whole charging cycle for both charging modes and look later on the log, say at what time was needed between 10% and 100%.