Synchronizing 59.94fps clips produces a 23.98fps synchronized clip

Hello everyone.

I am editing 3D fotage made with a GoPro.

The clips were shot at 720p60;

I want to use FCP X's synchronization feature in order to work on them.

But all I get is a 23.98 compound clip, for which I cannot change the frame rate.

Inserting it in a 59.94fps project results in less than 59.94fps but over 40fps!

ANyone with the same issue ... or an explanation?

Thanks in advance,

Jerome.