Hah! I figured it out. I have a daily task with subtasks. The subtasks were all marked as due yesterday and complete so they didn't show up. So the bug is not expansion but rather in the setting of the state of subtasks when the task is completed.
One thing I ran into today is that when I close Task Coach with a folder closed in a view I can't open the folder the next time I start Task Coach. Where is the folder state saved? I would like to edit that information by hand so I can see my subtasks.
Some things changed after another reboot. I created a bug report with more details. https://sourceforge.net/p/taskcoach/bugs/1676/
Many keys and clicks don't work correctly on Ubuntu 18.10 (cosmic)
I upgradeed to Ubuntu 18.10 and Task Coach 1.4.4 is mostly not working. Some specific failures: - New task doesn't do anything, from the menu or the Insert Key. - Control-Return and Shift-Return don't do anything for a single task or subtask, and both act like Edit for multiple tasks. There desn't seem to be a cosmic PPA for Task Coach.