How can I set multiple themes to an initiative?

[Jayne Roques]

I have Theme X, Theme Y, and Theme Z.

I have Initiative 1 which supports X, and Z.

In the PortfolioPlanView, hierarchy level set to Initiatives.

The Theme column is visible and there is a choice of X, Y, and Z.

I can select any one theme, but I can't select more than one theme.

I've tried holding control, holding shift, holding alt, and combinations but I've not been able to select X and Z.

[Jayne Roques]

Answer supplied elsewhere: 
A story can have only one theme, but epics and Initiatives can have multiple stories, each with one theme.

If Story A supports Theme X, and Story B supports Theme Y, the epic/initiative that contains Story A and Story B now supports Themes X and Y.

You can't set multiple themes at the Initiative/Epic level because they wouldn't map correctly to the stories.