I am using MySQL Workbench 6.3.7 build 1199 CE (64 bits) on a Mac with OS X Yosemite 10.10.5. I am connecting to an Amazon RDS MySQL instance.
When I enter a simple
This is still an open bug in 6.3.8: https://bugs.mysql.com/bug.php?id=82231
The possible workaround is to open secondary tab with the same connection and work in there. However it crashes anyway from time to time.
Until the bug is fixed I use free Mysql Workbench aleternative for common work. For mac users I would suggest https://sequelpro.com.