To reproduce:

Create a Heading or button block and insert a merge tag from the Merge Tags dropdown. The merge tag is displayed with its "friendly" name with a dashed border, as expected (screenshot 1).

Then change the mouse focus to another block.

Instead of still displaying the friendly merge tag, it switches to display the raw value of the merge tag in the header or button block.

The expected behaviour is that heading and button blocks behave the same way as text blocks and the "friendly" merge tag label is displayed instead of the raw value at all times.