Actually Release 1.4.2 but that is not available above.
I noticed that as I got a bigger task database Task Coach got very slow - 4-5 second delay after every mouse click.
I finally figured it out. The default "save after every change" setting seems to be the problem. A save seems to be performed when you do things like expand or collapse tree items or simply open a task. With ~240 tasks this is quite unusable.
Unchecking the "save after every change" box seems to bring the performance back.
This to me seems a bug - surely saving the database every time you expand a tree item or open a task is not really necessary if it causes such problems.
I've got the exactly same behaviour, but with only a few douzen tasks and version 1.4.3