1. Add some files
2. Make cluster
3. Lookup (successful), all green and valid
4. Save - and now randomly stops after saving few files (sometimes zero, sometimes a few, all if I'm really lucky)

Count of pending files is valid (greater than zero). The title is gray.

closing picard and try again helps (but sometimes requires more than one try... - like 20 restarts to save all tracks).
Refresh + Save on album never helped.

Here is the log - all tracks except 5th are saved successfully.

D: 22:31:46 GET http://musicbrainz.org:80/ws/2/release/a249e6ee-f0aa-4e75-a09a-a0e31061f49a?inc=release-groups+media+recordings+artist-credits+artists+aliases+labels+isrcs+collections+artist-rels+release-rels+url-rels+recording-rels+work-rels
D: 22:31:47 Received reply for http://musicbrainz.org:80/ws/2/release/a249e6ee-f0aa-4e75-a09a-a0e31061f49a?inc=release-groups+media+recordings+artist-credits+artists+aliases+labels+isrcs+collections+artist-rels+release-rels+url-rels+recording-rels+work-rels: HTTP 200 (OK)
D: 22:31:47 Loading release u'a249e6ee-f0aa-4e75-a09a-a0e31061f49a' ...
D: 22:31:47 New CoverArt for <Album a249e6ee-f0aa-4e75-a09a-a0e31061f49a u''>
D: 22:31:47 Cover Art Archive disabled by user
D: 22:31:47 Skipping cover art provider Cover Art Archive ...
D: 22:31:47 Cover art from Amazon disabled by user
D: 22:31:47 Skipping cover art provider Amazon ...
D: 22:31:47 Cover art from white list disabled by user
D: 22:31:47 Skipping cover art provider Whitelist ...
D: 22:31:47 Cover Art Archive disabled by user
D: 22:31:47 Skipping cover art provider CaaReleaseGroup ...
D: 22:31:47 Moving <File u'05 Sweet Nothing (Qulinez Remix).mp3'> from <Cluster u'Unmatched Files'> to <Track c060af22-3cea-43b7-81e8-b96d1e45742d u'Sweet Nothing (Qulinez remix)'>
D: 22:31:47 Album a249e6ee-f0aa-4e75-a09a-a0e31061f49a loaded: Calvin Harris feat. Florence Welch - Sweet Nothing
D: 22:31:50 Drop target = <Album a249e6ee-f0aa-4e75-a09a-a0e31061f49a u'Sweet Nothing'>
D: 22:31:50 Moving <File u'01 Sweet Nothing.mp3'> from <Cluster u'Sweet Nothing (Remixes) [feat. Florence Welch] - EP'> to <Track 18e68754-6b25-4e79-88ab-354f16f0b5c0 u'Sweet Nothing'>
D: 22:31:50 Moving <File u'02 Sweet Nothing (Ti\xebsto Remix).mp3'> from <Cluster u'Sweet Nothing (Remixes) [feat. Florence Welch] - EP'> to <Track 416f367d-9eed-4628-9cae-835cebb065b0 u'Sweet Nothing (Ti\xebsto remix)'>
D: 22:31:50 Moving <File u'03 Sweet Nothing (Burns Remix).mp3'> from <Cluster u'Sweet Nothing (Remixes) [feat. Florence Welch] - EP'> to <Track c6eb37e9-a422-4c2f-90c7-7d1025650b22 u'Sweet Nothing (Burns remix)'>
D: 22:31:50 Moving <File u'04 Sweet Nothing (Dirtyloud Remix).mp3'> from <Cluster u'Sweet Nothing (Remixes) [feat. Florence Welch] - EP'> to <Track eadc2ead-bfdd-47f8-b7d9-037c811ae56e u'Sweet Nothing (Dirtyloud remix)'>
D: 22:31:50 Removing <Cluster u'Sweet Nothing (Remixes) [feat. Florence Welch] - EP'>
D: 22:32:11 Updating file <File u'01 Sweet Nothing.mp3'>
D: 22:32:11 Updating file <File u'02 Sweet Nothing (Ti\xebsto Remix).mp3'>
D: 22:32:11 Updating file <File u'03 Sweet Nothing (Burns Remix).mp3'>
D: 22:32:11 Updating file <File u'04 Sweet Nothing (Dirtyloud Remix).mp3'>
D: 22:32:11 Saving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/01 Sweet Nothing.mp3'
D: 22:32:11 Updating file <File u'05 Sweet Nothing (Qulinez Remix).mp3'>
D: 22:32:11 Moving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/01 Sweet Nothing.mp3' => u'/mp3/Calvin Harris feat. Florence Welch/Calvin Harris feat. Florence Welch - Sweet Nothing (2012)/01 Sweet Nothing.mp3'
D: 22:32:11 Saving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/02 Sweet Nothing (Ti\xebsto Remix).mp3'
D: 22:32:11 Updating file <File u'01 Sweet Nothing.mp3'>
D: 22:32:11 Moving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/02 Sweet Nothing (Ti\xebsto Remix).mp3' => u'/mp3/Calvin Harris feat. Florence Welch/Calvin Harris feat. Florence Welch - Sweet Nothing (2012)/02 Sweet Nothing (Tiesto remix).mp3'
D: 22:32:11 Saving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/03 Sweet Nothing (Burns Remix).mp3'
D: 22:32:11 Updating file <File u'02 Sweet Nothing (Tiesto remix).mp3'>
D: 22:32:11 Moving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/03 Sweet Nothing (Burns Remix).mp3' => u'/mp3/Calvin Harris feat. Florence Welch/Calvin Harris feat. Florence Welch - Sweet Nothing (2012)/03 Sweet Nothing (Burns remix).mp3'
D: 22:32:11 Saving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/04 Sweet Nothing (Dirtyloud Remix).mp3'
D: 22:32:11 Updating file <File u'03 Sweet Nothing (Burns remix).mp3'>
D: 22:32:11 Moving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/04 Sweet Nothing (Dirtyloud Remix).mp3' => u'/mp3/Calvin Harris feat. Florence Welch/Calvin Harris feat. Florence Welch - Sweet Nothing (2012)/04 Sweet Nothing (Dirtyloud remix).mp3'
D: 22:32:11 Saving file u'/dl/Sweet Nothing (Remixes) [feat. Florence Welch] - EP/05 Sweet Nothing (Qulinez Remix).mp3'
D: 22:32:11 Updating file <File u'04 Sweet Nothing (Dirtyloud remix).mp3'>

Note: I had the same behavior on 1.3 (that's why I checked bleeding edge version from git)

Please ask If I can provide any additional data that would be helpful.