As of February 1st, 2017
GIMP 2.8.20 is the current stable release.
I haven't updated yet,
I'm still running GIMP 2.8.19.
which has been working just fine for me.
Perhaps updating your gimp,
with the most recent version will solve this issue?
However.
I would avoid reusing your current GIMP User Profile,
with any new installation of GIMP.
One more thing you can try.
Is to create a new GIMP User Profile.
Most of the time,
creating a new GIMP User Profile.
Can correct many issues within GIMP's interface.
You can create a new GIMP User Profile,
by renaming the current profile.
For example:
if I were to rename my current profile.
Located at "C:\Users\Wallace\.gimp-2.8"
I would rename it something like,
.gimp-2.8_old.
Once you rename your current user profile.
Starting GIMP will create a new GIMP User Profile.
You can then see if this behavior continues with the newly created profile.
If it doesn't,
then it was something within the Old profile,
which was causing the issue.