We also have the exact same issue.  Our main user always sees customers in hierachical view.  The rest of us would like to see it that way too but we have to manually change it EVERY time.  Even if we are still working in the same customer, it immediately goes back to flat view just after one action.  We are all very frustrated with this.  Our staff has tasked me with finding the answer as to how we can change our settings to keep it in hierarchical view.  We assumed you could change it in settings, view or preferences but we can't find anything that works.  Please help!