The choice to use the private setter was a defensive one as the public

setter prevents being called multiple times (though does short circuit
if an identical input is provided, which I think is actually true here,
therefore the public one is probably functional (and a no-op).)

It is not clear to me on analysis how the unit information is or was
lost. A quick test commenting out these two lines which reset
converter/units displayed no obvious detrimental effect to removing
them, suggesting that even if once they were necessary, they may no
longer be.

These lines were last touched in #24141, though that really only generalized
the code into a loop rather than copy/pasted x and y behavior.
The original inclusion of resetting was in #4909, which indicated that
the dialog reset unit info. AFAICT, that is no longer true, though I
have not rigorously proved that.

Originally posted by @ksunden in #28970 (comment)