Real estate agent allowed tenants to move in prior to start of lease w/out telling us

[Joe Tanner]

Our property management company seems to contract with a real estate agency when there is turnover on tenants.  We just had a 6 year tenant move out and new tenants move in.  The problem started after we signed a lease for 1 March but received notification from the electric company that the new tenants were switching the electricity to their name on 23 Feb.  I e-mailed the real estate agent who worked the lease to see what was going on and he said he'd get back to me and never did.  Then we got a message from the actual property management company saying some repairs that were being done were completed and the tenants were set to move in on the 24th.  

We have two real concerns.  1) The agent either did a poor job keeping us informed or intentionally with held information.  2) Liability with tenants living in our property without any documentation on the agreement.

I requested an addendum to the lease with the move in date and the pro-rated fee that would be charged.

Is this sort of practice common in real estate where people move in before the contracts are signed?