This bug arose while characterizing TPC-DS tests that flap.
Runs of the full TPC-DS suite display results for various tests that variously fail or succeed in absence of code or environment changes. All failures are connected with displays of the scale of decimal values. Some tests contain SET DECIMAL_V2=1; statements. I theorized that this option was getting left on in SQL connections and exposed to subsequent tests.
The main test suite driver file, $IMPALA_HOME/tests/common/impala_test_suite.py, contains logic to reset options in the SQL session between tests, however its regex to detect these statements fails for statements that contain digits (SET_PATTERN = re.compile(...)).