Unable to uncheck "display as bkg"

[RayMarble]

There's one string object in my frame that has the "Display as background" ghosted. Other options work as expected (visible at start, save background etc); also other string objects are normal ("D. a. b." can be ticked / unticked) except for this one string.

I tried everything I can think of, but nothing helps - if it (or the layer containing it) was locked or something I shouldn't be able to click on it in the first place, right?

And yes, using latest build here etc.

[Jeff]

Can you email me over the file so I can check it out?
I don't know whats going on with that.

[RayMarble]

Sent!

The file isn't commented or anything (it's empty anyway), hope it's just a case of me overlooking something obvious.

[Yves]

Maybe this string has a movement? I think this option is disabled for objects that have a movement.

[RayMarble]

I just got a reply from Jeff too! Thanks guys, turns out that's exactly the case.