I can confirm the same issues with MC17 & 18 as Dr Tone and other users have reported on this and other threads as well.
As it stands, Syncing via MTP on Android 4.x is problematic, to say the least.
*MC Takes forever to "load" the contents of an android device using android 4x and MTP mode. It can take up to 10minutes to actually load my SGSIII with a class 10 sd card.
*Syncing throws up errors while uploading, making the MTP application on the phones get stuck
*MC Will ignore any files currently present on the device and will try to sync everything back again. Tested with both mp3 re-encoding and external encoder (neroaac)
There are other posts in this board with this kind of issue and i think it's now a good opportunity for this matter to get some more attention, so you guys be able to fully resolve it.
Other Threads with problems syncing over MTP on android Phones:
Sync with MTPSyncing to Galaxy S2Samsung Galaxy S3 - Sync issuesCan't sync after ICS update on Droid4