In the manual testing run on Solaris 11 (INTJDK-7624025) was revealed behavior fixed in JDK-4410243.
Run the attached test in GTK LaF; change "100 100" in the text field to "22 51" and press Enter. Size of the JTextArea will change to 22x51, and in a second or so it will flicker exactly as described in JDK-4410243, changing from text area with a scrollbar and without one and back.
Note that on Solaris 11 a default GTK theme is Nimbus. Elsewhere I don't see it; perhaps this flicker effect depends on that since I cannot reproduce the behavior anywhere else.