When downloading large torrents to an ntfs-3g partition ktorrent UI periodically blocks for a long time (tens of seconds). Keyboard and mouse events are buffered until UI unblocks for a few seconds and after that it blocks again. This happens while the torrent is being downloaded; UI becomes responsive again when the torrent finishes downloading. The UI is not blocked when seeding torrents from an ntfs-3g partition.

Reproducible: Always

Steps to Reproduce:
1. Add a large torrent (30 Gb or more) to ktorrent and choose an ntfs-3g partition as the target. Make sure it starts downloading (i.e. ktorrent is receiving data).
2. Try interacting with ktorrent UI. E.g. click on different torrents in the download list, open contextual menu, click on the File/Edit/View... menu, etc.


Actual Results:  
At certain points UI blocks, without CPU load. HDD seems not loaded as well. While UI is blocked, network transfers are not happening (network receive and send meters drop to 0).

Expected Results:  
The UI should remain responsive at all times. Preferably, network transfers should also remain active. At least some torrents may be on different filesystems and not blocked by write operations.

I have saved and attached a backtrace of ktorrent while it is blocked.

Kubuntu 15.10, x86_64.