This is probably due to the Hotspot settings you have chosen.
Open the tabbed dock settings by right-clicking it and selecting dock settings.
Now click on the Hotspots tab. There are two things you can due to correct this, first you can completely take the hotspot away so it will never happen, or you can set the delay to maximum, but then you'll still have the dock pop up if you keep your mouse down there long enough.
To completely take the hotspot away, just click the "white" arrows in the dialog you see and then click the drop-down menu. Once here, select the option that says "Due nothing to this tabbed dock". There are three arrows along the bottom, so make sure you do this for all that are "white" or active.
To set the activiation delay instead of getting rid of the hotspot, click the arrow on the screen where you want the hotspot and then set the "Activation Delay (for all) scroll bar all the way to the right or "Very Long".
Hope that fixes the issue.
