How to reproduce (helps if you record OS-level pointer output, e.g. libinput debug-events):

1. Put pen in a corner
2. Lift pen out of range
3. Put pen in middle
4. Notice that reentry significantly overshoots for a brief moment

Can probably be mitigated by resetting last vector to current vector on reentry (likely requires functional OutOfRange reporting by the tablet parser, assuming tablet support), or by timestamping reports and allowing the user to specify the interval at which the filter should self-reset, or by not filtering on extreme coordinate changes.