it appears that jtreg doesn't support having multiple entries for the same test in one problem list (see CODETOOLS-7902481).
the following occurrences in jdk problem lists should be merged in order to achieve the expected behavior:

test/jdk/ProblemList.txt:java/awt/Frame/FramesGC/FramesGC.java 2
test/jdk/ProblemList.txt:java/awt/Modal/OnTop/OnTopModal6Test.java 2
test/jdk/ProblemList.txt:javax/swing/JComboBox/8032878/bug8032878.java 2