libmtp-1.0.0 breaks mtp support with media-sound/banshee-1.4.3-r2 on my machine. The device will mount in banshee but no songs or videos are detected on the device. This is a regression from the previous versions where banshee functioned properly. I suggest changing banshee's dependency to depend on the 0.3.7 ebuild of libmtp as a solution.
FYI this is fixed upstream in banshee 1.5.1. See this bug : https://bugzilla.gnome.org/show_bug.cgi?id=594191
seems fixed with media-sound/banshee-1.6.0
*** Bug 294477 has been marked as a duplicate of this bug. ***