0.5.1 is primarily a bug fix release, but also includes some early features from 0.6 development. Major bug fixes are highlighted in bold.

1. The identd plugin now works
2. The error manager now shows the elapsed time since the error occured, rather than the absolute time
3. The "nicklist alt background colour" and "treeview rollover colour" options now use a single setting, rather than one to enable and one to set the colour
4. Added a /saveconfig command
5. The /set command now has an --unset switch
6. Actions can now be disabled by setting actions.killswitch to true
7. The preferences dialog now saves optional colour settings properly
8. Fix a rare exception in the error manager dialog
9. The nicklist alt background colour and all treeview colours now update as soon as their config settings are changed
10. Added a migration wizard to re-extract actions and plugins if they've been updated
11. The error manager now shows more detailed status information
12. Added default aliases for op, deop, voice, devoice, kickban and unset
13. Fixed an exception in the Now Playing plugin
14. The formatter now catches exceptions better and provides more detailed error information
15. Added mode aliases for plexus/rizon
16. Added formatters for plexus' help responses, and extra whois fields
17. The preferences dialog now indicates a client restart is needed to change the Look and Feel
18. Receiving a names reply for an unknown channel no longer throws an error
19. URL linking is now more intelligent and can often strip off unwanted trailing punctuation
20. More options are now cached, so the client should use less CPU time
21. The title bar of maximised windows no longer reappears after the UI is reset
22. Added support for notification groups and intelligent notification targets - this allows (for example) all whois output to be sent to the last window where a whois command was issued for the relevant user
23. Duplicates of DMDirc's default settings are no longer stored in the user's configuration file
24. DMDirc now attempts to save its config files properly if it is unexpectedly shutdown (e.g. terminated by a task manager)
25. Added -r command line option to disable error reporting for that session
26. The actions editor no longer allows invalid or empty file names
27. Fixed exception in some dialogs when they didn't have a saved state
28. The status bar error icon now shows the highest severity error that hasn't been viewed, rather than displaying each error for 10 seconds
29. Fixed some plugins' default settings not being registered properly
30. The perform panel in the Server Settings dialog now saves correctly
31. Added a setting to make DMDirc confirm when it's being closed
32. Fixed rare issue where the active treeview node got set to a notification colour
33. Added a plugin configuration menu
34. The actions condition editor now shows the correct comparisons
35. The links in the about dialog now open correctly
36. Treeview colours now fall back to proper values if they're not set
37. The preferences dialog now sets the right options for the nicklist colours
38. The list modes panel in the Channel Settings dialog is now disabled correctly if there are no list modes
39. Potential fix for a rare exception when right clicking in the nicklist
40. Fixed bug where a single line added to an empty textpane would not be drawn straight away