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. However, Microsoft amended its policy, which can be found here. Despite the change in policy 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. As a result we don't support browsers running in compatibility mode. It is advised to rather use Edge mode.
If you are using a supported browser version but compatibility mode has been enabled, the compatibility mode can be switched off or K2 smartforms can be excluded from the list of websites where compatibility mode is applied. This can be configured via the Compatibility settings or via Enterprise mode.

Compatibility Mode

Compatibility mode in Internet Explorer is a feature that helps you view webpages that were designed for previous versions of the browser, however having it enabled can break newer sites that were designed for modern browsers.

Enterprise Mode

Enterprise mode allows full control of browser compatibility settings using a local / URL to an xml file. This can be enabled via group policy and will allow enterprises dependent on IE8 infrastructure to upgrade to IE11 without changing any code. It is also highly dynamic and can be adjusted on demand without group policy updates.

Removing K2 smartforms from Compatibility Mode

K2 smartforms can be removed from Compatibility mode by disabling the view settings or removing K2 smartforms from the list of websites added to Compatibility View.
To do this navigate to Tools menu -> Compatibility View Settings

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Deselect display intranet sites in compatibility View and make sure that the K2 smartforms sites are removed from the list of websites added to Compatibility View.

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See the following link for more information on how to remove K2 smartforms from Compatibility mode (Internet Explorer 8):
http://blogs.msdn.com/b/askie/archive/2009/03/23/understanding-compatibility-modes-in-internet-explorer-8.aspx
Details on how to configure these settings via group policy:
https://msdn.microsoft.com/en-us/library/dn321457.aspx

Configuring K2 smartforms with Enterprise Mode

K2 Smartforms should be configured within the Enterprise site list to run in “Edge Mode” or the Enterprise site list feature should be disabled.

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See the following links: