Internet Explorer 8 (including any other Internet Explorer version running in IE8 compatibility mode) has been deprecated as a supported runtime and design time browser in K2 smartforms 4.6.9 based on Microsoft’s communication to end support for IE8 on or before January 2015…. SmartForms will no longer support IE8 from K2 smartforms 4.6.9 onwards. If you continue to use IE8 after this release, some new or existing features and functionality may no longer work as expected. Any bugs or performance issues that occur only when using IE8 will not be investigated or fixed after this release.
Prior to 4.6.9, K2 blackpearl would support IE8 in runtime only — judging from previous blackpearl compatibility matrices, it seems IE 8 was never supported as a design time browser.
What makes this change so important is precisely because IE 8 shipped with Windows 7. According to netmarketshare.com, Windows 7 was the desktop operating system of choice in over half of businesses it surveyed as of last month. The same website suggested that IE 8 has enjoyed a 20% market penetration between April, 2014 and February, 2015, while IE 11 has a steadily increased in adoption over the same time frame to 23%.
By the way, IE 8 was also the default browser in Windows Server 2008 R2.
Once you move up to 4.6.9, consider keeping an eye out for problems from business users on Windows 7 machines — particularly newly re-imaged ones.