ADDITIONAL SYSTEM INFORMATION :
The bug is reproducible on Linux and Windows OS on Java version 11 and 8. There is no known version of Java, where the returned result is as expected.

A DESCRIPTION OF THE PROBLEM :
When the first parameter (LocalDate) is the last day of February in a leap year (e.g. 2020.2.29) and second parameter last day of February in a non-leap year (e.g. 2021.2.28), method Months.between() return 11 and YEARS.between returns 0, although, in my opinion, it is the full year in between.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
To reproduce, simply just calculate the number of months/years between two dates (using LocalDate) where the first parameter is last of February on leap year and the second parameter is last day of February on a non-leap year.
MONTHS.between(Temporal, Temporal);
YEARS.between(Temporal, Temporal);

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
For: System.out.println(MONTHS.between(LocalDate.of(2020, 2, 29), LocalDate.of(2021, 2, 28))); expected result is 12.
For: System.out.println(YEARS.between(LocalDate.of(2020, 2, 29), LocalDate.of(2021, 2, 28))); expected resutl is 1.
ACTUAL -
For: System.out.println(MONTHS.between(LocalDate.of(2020, 2, 29), LocalDate.of(2021, 2, 28))); actual result is 11.
For: System.out.println(YEARS.between(LocalDate.of(2020, 2, 29), LocalDate.of(2021, 2, 28))); actual resutl is 0.

---------- BEGIN SOURCE ----------
System.out.println(MONTHS.between(LocalDate.of(2020, 2, 29), LocalDate.of(2021, 2, 28))); // prints out 11, not 12
System.out.println(YEARS.between(LocalDate.of(2020, 2, 29), LocalDate.of(2021, 2, 28))); // prints out 0, not 1
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
The only workaround is to add the additional check in the code if the first parameter of the method in last of February in a leap year and then add one day to the second parameter of the method.

FREQUENCY : always