I have a lot of custom views set up in Outlook and experience the
following really annoying issue: Sometimes I accidentally click onto
the header of my task list and Outlook automatically sorts all tasks
by the field that I just happened to click on. So, every time this
happens I have to go back into Current View and reset the sorting
order that I previously had in there. Is there any way to stop Outlook
from doing that? I don't want it to sort anything if I click on any of
the task field column headers.

I am using Outlook XP and Outlook 2003.

You're essentially asking Outlook to not do what it's programmed to do
for the convenience of the masses, the inconvenience of the few.
Respectfully, this is a DDT issue. (Don't Do That). OTOH, there is a
way to customize your toolbar, dragging a drop-down-list of available
views to the toolbar to minimize the clicks required to restore the
customized view...