This is not a defect or a problem. Your battery firmware or software driver is probably configured to forego charging when the battery is very near to 100%, to save on charge cycles. Rechargeable batteries have a limited lifespan, and repeated charging can shorten it. Charging the battery also heats it up, which can shorten its lifespan. The firmware is just trying to protect you from these and increase the lifespan of the battery.
If this situation is unfamiliar to you, then it is likely that you have used devices in the past which report false charge levels to the user. For example, some devices will say that they are "100%" charged, even though the battery's theoretical maximum capacity has not been completely filled up. This user interface trick is sometimes used to prevent consumers from being concerned by exactly the symptoms of a non-problem which you are seeing.
1And if you want to prove this to yourself, let it discharge below 95% or so (the line usually seems to be there and your screenshots support this) and it should start charging when you plug it back in. – Shinrai – 2013-01-07T16:37:33.787
1This is the case with my Lenovo and easy to test as noted bt @Shinrai – Dave M – 2013-01-07T16:43:23.730
2
Correct diagnosis, incorrect reason. Battery "memory" is specific to NiCd batteries only. Lithium batteries do not exhibit memory effect, in fact they often perform better when recharged at 25-50%. However, all rechargeable batteries do have a limited lifespan, and it is related to the number of charge cycles. The battery/charger are attempting to protect the battery by reducing the charge cycles when not specifically necessary. It may also be to reduce heat in the battery, which also shortens lifespan.
– techturtle – 2013-01-07T17:24:08.500I agree with @techturtle upon doing further research. Can someone please suggest or make an edit to my answer that incorporates this knowledge? Thanks. – allquixotic – 2013-01-07T17:39:55.530