Forcing a Task Start Date Causes Over Allocations

I'm a fairly new SS user, but have experience with MS Project. I have a task that, based on predecessors starts on a date that is earlier than when a shared resource is available. What is the best practice for assigning a "forced" start date?

When I attempt to force this one start date on a single task, the result is several over allocations. Does SS not recalculate the timeline based on remaining predecessors? Why does it choose to over allocate the resources instead of recalculating the sheet to match the resource availability?