I found the problem (and am working on a solution).
0.4.12 and 0.5.0 exhibit the same behaviour.
However the problem only occurs when you have a backup server defined (fill server).
My guess is that your 0.4.12 setup has no backup server, but your 0.5.0 setup does.
Freezing while loading NZB
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Re: Freezing while loading NZB
Unfortunately, do not distinguish the two configurations. I use the backup server for quite a long time. Obviously there is another cause.
Sorry for the bad news
Sorry for the bad news

Re: Freezing while loading NZB
maybe some helpfull observations:
(no Backup Server) first value for 0.4.12 second value for 0.5.0
started clean & empty 15780 K 17944 K
1 nzb file (Queue Size 33 GB) - sabnzbd+ pause mode 21840 K 20460 K
1 nzb file (Queue Size 33 GB) - sabnzbd+ running ~25860 K ~44700 K
23 nzb file (Queue Size 965 GB) - sabnzbd+ pause mode 118872 K 41412 K
23 nzb file (Queue Size 965 GB) - sabnzbd+ running after restart ~42000 K ~57500 K
23 nzb file (Queue Size 965 GB) - sabnzbd+ running after 2. restart after 10 min ~42000 K ~42500 K
(put 1 backup server real time in)
23 nzb file (Queue Size 965 GB) - sabnzbd+ running - no GUI response for > 30 minutes then i kill the process [~500000 K - 900000 K] [~500000 K - 900000 K]
23 nzb file (Queue Size 965 GB) - sabnzbd+ running - no GUI response after restart then i kill the process [~500000 K - 900000 K] [~500000 K - 900000 K]
23 nzb file (Queue Size 965 GB) - sabnzbd+ running - delete the backup Server in sabnzbd.ini ~42000 K ~42500 K
so it looks like that both versions handle the memory equal. I could not say in the moment why i see earlier a difference
(no Backup Server) first value for 0.4.12 second value for 0.5.0
started clean & empty 15780 K 17944 K
1 nzb file (Queue Size 33 GB) - sabnzbd+ pause mode 21840 K 20460 K
1 nzb file (Queue Size 33 GB) - sabnzbd+ running ~25860 K ~44700 K
23 nzb file (Queue Size 965 GB) - sabnzbd+ pause mode 118872 K 41412 K
23 nzb file (Queue Size 965 GB) - sabnzbd+ running after restart ~42000 K ~57500 K
23 nzb file (Queue Size 965 GB) - sabnzbd+ running after 2. restart after 10 min ~42000 K ~42500 K
(put 1 backup server real time in)
23 nzb file (Queue Size 965 GB) - sabnzbd+ running - no GUI response for > 30 minutes then i kill the process [~500000 K - 900000 K] [~500000 K - 900000 K]
23 nzb file (Queue Size 965 GB) - sabnzbd+ running - no GUI response after restart then i kill the process [~500000 K - 900000 K] [~500000 K - 900000 K]
23 nzb file (Queue Size 965 GB) - sabnzbd+ running - delete the backup Server in sabnzbd.ini ~42000 K ~42500 K
so it looks like that both versions handle the memory equal. I could not say in the moment why i see earlier a difference

Re: Freezing while loading NZB
I have a solution that will go in 0.5.2 (0.5.1 was canceled).
0.4.12 has the same bad behaviour as 0.5.0 and also triggered by the backup server.
This bug has been in there for years (from before the current team took over).
Nobody else noticed it, or at least did not relate high memory usage with backup servers.
There is a chance element involved, due to the ordering of the servers in the INI file.
If a backup server is listed before a primary server, the memory problem is more likely to occur.
With 0.5.0 it looks like the problem always occurs.
0.4.12 has the same bad behaviour as 0.5.0 and also triggered by the backup server.
This bug has been in there for years (from before the current team took over).
Nobody else noticed it, or at least did not relate high memory usage with backup servers.
There is a chance element involved, due to the ordering of the servers in the INI file.
If a backup server is listed before a primary server, the memory problem is more likely to occur.
With 0.5.0 it looks like the problem always occurs.
Re: Freezing while loading NZB
nice to read, that this will be shortly fixed 
