Hi! I have similar problem and have found this topic

The reason is what UIPopupList do not updating it's label value for default pressetted value in editor.
In my example I have 2 popups on one screen:
1) "Difficulty" with coorsponding presets via Editor "Normal" and "High" (default "Normal")
2) "Language" with presetted value "English"
Then on game start all UIPopupList-s are cleared and refilled via code, but mSelectedItem is already set to "Normal" and "English" correspondingly. And if my selected value for any of this 2 popups will be the same as presetted, then there is will not be any corresponding UILabel value update and I'll see UILabel's default "value here" text.
For the time as the hack I've added 2 strings in the end of UIPopupList.Start function:
if (mSelectedItem != null)
TriggerCallbacks();
...but I feel this is not the best solution, coz there is already could be some callbacks with unwanted extra call.