OS X 10.11.4 has been publicly available for a month now; here is a list of its bugs of which I am aware.
Finder – incorrect column width
This can occur when using Finder windows which are set to column view. When switching folder in the view, the rightmost column being displayed has excessive width, filling the Finder window, its divider being placed incorrectly at the right edge of that window.
This long-standing but intermittent bug dates back to Mavericks if not earlier, and I have whinged about it here and here, and listed it as present in 10.11.2 and 10.11.3. The only workaround is to select a different folder, then to select the correct folder again.
Core Foundation library – loss of drag and drop
I am beginning to wonder if this long-standing bug might have been fixed, as I cannot recall when it last happened. Or perhaps I am now too scared to use drag-and-drop as much as I used to.
Energy Saver pane – inconsistencies in controls
The features available in the Energy Saver pane of System Preferences are inconsistent between Macs, and incomplete, for example not providing a separate control slider for system sleep on some hardware. Further details are here. These remain in 10.11.4 just the same as in 10.11.3 and 10.11.2.
The only workaround is to use a third-party tool such as MacPilot to edit the preferences instead of the bundled pane.
Power Management – hard drives always put to sleep on system sleep
On some recent iMacs at least, Power Management ignores any setting to not put hard drives to sleep: when system sleep occurs, the hard drive in an internal Fusion Drive is always put to sleep, regardless of the drive sleep setting. This is detailed here.
The only workaround is to set the system sleep time to Never, which also stops hard drives from being put to sleep.
OS X internals – clicking on a window causes it to jump
When switching between apps by clicking on a window, sometimes the selected app comes to the front and its window jumps to a new position on screen. I used to think that this was confined to certain apps such as Tweetbot, but it also affects Apple’s Messages app and others, and persists in 10.11.4.
The workaround is to switch to that other app by clicking on its icon in the Dock.
Trackpad – unexpected shift of text insertion point
This is another long-standing bug, which goes back to the early days of Apple’s Magic Trackpad in about 2010. You are typing along happily, with your hands well clear of the trackpad, and suddenly the text insertion point jumps to a different location in the text which you are editing. This is sporadic and completely unpredictable, but affects a wide range of different apps, and still affects 10.11.4.
There is no workaround.
Disk Utility – failure to change partition size because of “partition (map) too small” error
I don’t know whether this old bug persists in 10.11.4.
Sporadic freezing, requiring a forced or automatic restart
Some models, notably MacBook Pro Retina, 13″, Early 2015 (MacBookPro12,1) and possibly iMac Retina 5K, 27″, Late 2015 (iMac17,1), freeze periodically and will either restart automatically, or if that fails they require a forced restart. This appears to be new with 10.11.4.
This appears to occur out of the blue, but is most common when browsing in Safari, even when using Apple’s Safari Technology Preview. I appears to relate to graphics drivers or a similar component close to the kernel. Further details are here.
There is no workaround.
[Added 15 May 2016.]
Please add your own experiences and I will incorporate as necessary…