Are you using Premiere Pro CC?
How is the footage being interpreted? In the Project Window, right click on a clip, and select Modify>Interpret footage. Check the frame rate options shown.
what are your Settings for the Sequenz/Timeline?
which frame rate is your master frame rate 25 or 50?
Perhapse the 25fps files are the film frame rate
and the 50fps are for little slomos (correct where than 50fps in a 25fps camera timeline)
Are you still having this problem? Please let us know.