Diagnosis
The unit is likely in continuous drain mode, which bypasses the bucket-full auto-shutoff. It'll run forever until you either switch it back to bucket mode or hook up a drain hose properly.
How to Fix It
Let's check the mode. 1) Look at the control panel on top. 2) Press the 'Drain Mode' button until the bucket icon (with a drop in it) is lit up, not the hose icon. 3) If the hose icon was lit, that was the issue. The unit should now stop when the bucket is full and the 'Bucket Full' light comes on.
If That Didn't Work
The bucket might not be seated correctly. Pull it out, check that nothing is blocking the slot, and push it back in firmly until you hear a solid click. A misaligned bucket won't trigger the float switch that tells the unit it's full.
Heads Up
If you want to use a hose, you have to physically attach it to the port on the back and then select the hose drain mode. Otherwise, it'll just pump water onto your floor.