Excess CPU usage when Open Files dialog is visible

I was getting CPU 150% in Activity Monitor on the Mac with an Open File dialog visible. Close the dialog and the % goes down to 3 - 4%, which is the background activity of my program. What I finally found was that if I turn off all of the QTimers in my program when the Open File dialog is open, CPU % goes down to about 1%.
There must be a bug that gets Qt into a loop of some kind if a Timer goes off (or maybe its the signal from the Timer) when the dialog is open.
Lots of discussion online about this, but nothing I saw said anything about QTimers affecting the problem.