In Melodic, we decided go with OpenCV 3.2. Since that is available from the system on Ubuntu 18.04, we didn’t have to build it ourselves and we just use the system version.
Not unless there is a very compelling reason to do so. In past releases when ROS bundled OpenCV itself, it led to a lot of problems and a lot of churn. Thus, we are going to try to stick with the system version of OpenCV for Melodic to avoid these problems.
It’s probably worth reaching out to the OpenCV and/or GTK community to see what the current situation, since the original bug in GTK seems to have been fixed 3 years ago. There is clearly something else going on. Unfortunately I don’t personally have much knowledge of either of those communities (or of the software).
Barring that, it may be worthwhile to go with the workaround you described in the above bug.
Hope that helps.