BackEnd Database Locking when FrontEnd runs a query - why?

The simple question is,

Why does a select query using the IN command lock the target database?

I am trying to write a reporting app where the users have a fairly skinny
frontend on their local machine. The frontend has tables that are linked to
a backend database that drive the application.

In the backend, I do all the work of querying various datasources around our
network to present user datasets.

The Frontend executes : select * from BE_Query in 'Backend'

The problem is, I need to be working in the Backend, creating new datasets,
creating reports, etc. Whenever anyone is using their FrontEnd, i can't
save anything to the Backend.

Any Ideas?

Thanks,
Matt