K2 5.1 (up to November 2018 CU FP5):
In K2 Designer, when configuring the "Show a tab" action you operate with tab names - you select the tab name and once selected, the tab name is displayed. But as soon as you close the rule edit dialog and open it again, it displays tab title. This is inconsistent.
If you work with tab names in UI while configuring the rule you would expect that the same should be displayed for saved rules.