Completly normal. The method that seems to be employed for the battery percentage is read the voltage itself and make a guess
This high voltage drops down quite quickly both as a "load" is applied to the battery,. Plus there is not a lot of change in capacity from the very high voltages to the more normal voltages, in any li-ion battery. So while the voltage can be used to guestimate a range of charge levels, between like 4.0 and 4.3 there isnt much changed in the battery itself.
Further from what i have seen so far (not totally sure) they are charging to 4.35v which is a rescent slight change in the chemistry of the li-ion to allow for higher charge levels without it gassing or reducing the life (Havent tested that theory long enough yet either).
Also All li-ion alogrythms for charging do a CC CV charge, where the final charge is just "holding" the voltage at the high, till the batterys charge state floats up to that level. This can (not facted out yet) mean that leaving it on the charge past the time it claims it is fully charged , it will put tiny bits more into it. This happens more with my big fat zerolemon battery because it seems to have more resistance to the other connected cell items than would be desired.
Anyways all is well, just dont believe anything a computer tells you , and it will be fine
The other methods have thier own deficiencies.
Li-Ion batteries really do not prefer to be left at their high charge voltages, as they degrade faster there. so when you read the above, or try "bump" charging methods (thats just restarting the charge) It is not good for it. The battery will be happier, using it like it was designed, taking it off the charge when it states it is full. all of this being more info than anyone needs to know, or freaking care about.
As a li-ion battery becomes old and weak, it will exhibit even more of these charateristics that have people wondering. It will drop off the highs quicker still, have less total capacity, and increse a tiny bit in resistance , which will cause it to drop even more under load. At some point the battery would be so bad at that, you would want to replace it.
Heat, the li-ion cells dont like these extreeme heats. they prefer to work more at normal room temps and cold but not extreeme cold. So take that in also as a factor in keeping your battery more happy, again if you want to waste half your life pampering the thing