Question: Typesetting labels of derivatives in plots

I'm trying to add a label to a plot and need the derivative to be represented as a dot. My typesetting rules are set to extended, and it works in a worksheet but not in the plot. See attached image. The code to generate it is:

#the output is shown with a dot over phi
diff(phi(t),t);

#derivative in label not shown as a dot
plot(sin( t), t=0..10, labels=["t", typeset(diff(phi(t),t))], labeldirections=[horizontal, vertical]);

any ideas?

thanks

EDIT:

this seems to work... ( i will leave this question here as it might come in handy to someone else).

plot(sin( t), t=0..10, labels=["t", Typesetting:-Typeset(diff(phi(t),t))], labeldirections=[horizontal, vertical]);

Is it a bug that using the first variant does not work? any ideas from the experts?