How do I insert a strikethrough iota into a FrameMaker 2015 equation?

In FM 2015, I can no longer insert a strikethrough iota into an equation.

• I have a defined special character, but when I insert it the strikethrough kills the previous part of the equation.
• Previously, I could go into Start/stop string and do this. But now the strikethrough in the tool bar is greyed out, and selecting it in character designer does nothing. Furthermore, if I start the string, select "i" and change the font to symbol to get an iota, the insert string will not end, and the quotes are displayed in the equation!
• This used to work in my older FrameMaker