A DESCRIPTION OF THE PROBLEM :
Javadoc suggests the plus method adjust the Month by quarters, not by months.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
"Returns the month-of-year that is the specified number of quarters after this one. " should be reworded to be consistent with the https://docs.oracle.com/javase/8/docs/api/java/time/Month.html#minus-long- method (i.e. change 'quarters' to 'months')

e.g.
"Returns the month-of-year that is the specified number of months after this one. "
ACTUAL -
"Returns the month-of-year that is the specified number of quarters after this one. "

URL OF FAULTY DOCUMENTATION :
https://docs.oracle.com/javase/8/docs/api/java/time/Month.html#plus-long-