This should list all changes in Aegisub between version 2.1.8 and 2.1.9. A few minor things may have been missed, but it shouldn't be anything important.
The Attachments dialogue will now properly set undo points
When closing the Attachments dialogue, any empty attachment sections are cleaned up from the file
Fix a handle leak and a rare deadlock in the DirectSound audio player
Might be a little faster when displaying keyframe markers (pink lines)
No more "You pressed cancel!" pseudo-errors when canceling audio loading
Fix for rare furigana layout issue in karaskel
The append operation for the subtitle object now intelligently appends dialogue lines to the end of the Events section instead of absolute end of file, solving issues with appending dialogue after attachments
Returning selections from Lua macros now works correctly, no longer shifts the selection down by one from the intended
The table.copy_deep function in utils.lua now works as advertised and handles self-referencing tables and circular references
Added new "remember/recall" suite of functions to Karaoke Templater
Selecting charset/text encoding after opening a non-Unicode file now properly respects your choice
Added support for writing the EBU STL (tech 3264) subtitle data exchange format
Warn if trying to load a binary .sub file, which is likely a VobSub file (which is not supported)
Changed compilation settings to make the Windows binaries smaller without sacrificing speed or functionality
VSFilter is now linked as a normal DLL dependency instead of dynamically discovered at runtime, using alternative CSRI renderers no longer possible, this should make loading a wrong vsfilter almost impossible
Various input methods on Linux should work more reliably now
Fixed a variety of memory leaks
The locally installed help would never actually get used when using Help buttons or the Help menu
Fixed a bug where having a hotkeyable item having no hotkey would cause wrong key combinations (try to) activate that anyway
Various changes making it more stable, issues with Kapersky Internet Security 8 should be solved now
The portable version is now (again) a self-extracting RAR archive, rather than an InnoSetup installer
The active line is now always one of the selected lines after using the Select Lines dialog
Made the shift times history display one-based frame numbers when shifting the selection onwards
Updated list of "word separator" characters, meaning punctuation such as hyphens should now behave better
You now get an appropriate message when no dictionaries are installed and you try to spell check
Duplicating a style and renaming the copy no longer gives a rename warning
Fixes to copying styles between storage and script
All controls are now dynamically resized, as a result it is overall a little larger and adjusts size to fit translated texts
The subtitle grid now also takes the width of column title texts into account when calculating column sizes, allowing translations more freedom in choice of column texts
Fixed the "clicking near top/bottom of grid selects multiple lines" issue, and other row selection issues
The "make adjacent" threshold now has the end of the range be inclusive
Fixed a control layout issue on Mac, preventing it from working properly there
Added Polish
Added Farsi (Persian)
Fix a possible crash
Canceling FFmpegSource indexing now stops video loading, instead of trying another video provider
Fixed a bug related to first loading timecodes, then loading a video, causing subtitle rendering to break
Detached mode should work properly (again?)
Zooming video in works correctly again, it no longer compresses the video
As a side effect of the above, there is now no longer a sunken border around the video
The video display was consistently a little too small in each direction, causing blurry display
Other minor optimisations and improvements to error reporting
Fixed minor bugs with opening a new video without closing an already open one
The visual typesetting tools are now hidden when video is playing
Maybe made the OpenGL initialisation for the video display more reliable on poor drivers, might fix issues with some ATI/AMD and Intel driver versions