Yes, there is a bug in the update procedure. Amazing Charts is supposed to look at its current version number and determine if there is a newer (higher-numbered) version available (by "calling home" and asking the Amazing Charts Server - this happens when you start Amazing Charts).
But, due to a similar sort of error that led to the destruction of one of the Mars space missions, those using V6.0.9 (and earlier V6) won't get notified of the 6.0.10 upduate.
The actual problem is that when moving from Version X.X.9 to a X.X.10, Amazing Charts calculates (rightfully so) that 0.9 > 0.1 (since 0.1 and 0.10 and 0.100 are all the same in a mathmetical context). And V X.X.9 is > X.X.1, so as far as Amazing Charts is concerned, it is the latest version.
Unfortunately we forgot to explain to Amazing Charts that versioning is a different context. The result - those on V6 won't get notified automatically. (Though I'll soon add an announcement, which you'll see when logging into Amazing Charts.)
In any case, existing users wishing to upgrade can get the version at
www.amazingcharts.net/ac.