ORIGINAL: Sangeli
Ah! I see what you did. You assigned the pilot to the squadron with the "Get New Pilot" button. The script would not use that method of adding pilots; it adds veterans with the "Request Veteran" button then uses the release pilot button in the new view. And if you do it that way, you avoid the pilot experience drop. The fact that adding pilots this way doesn't result in an experience drop but every other way does suggests it's some sort of bug. But since you can't tell what type of plane pilots trained with it's probably for the best.
Well now I know this is a non issue. Thanks!
More testing (for the record, it's the 1123x10 Beta, but I don't think that matters). There are three ways to get a pilot out of the Reserve Pool, and they provide three completely different outcomes. From worst to best:
1) From the "Request Veteran" screen, click on the pilot's name.
Result: Experience Lost AND Chance of Delay (1-to-7 turns)
2) On the unit screen, use "Get New Pilot" button with "From..." set to "Reserve(##)".
Result: Experience Lost BUT No Delay (pilot moves immediately into the selecting unit)
3) From the "Request Veteran" screen, click the "Release Pilot" button (presumably the button associated with "Most Experienced").
Result: No Experience Lost AND No Delay (pilot moves immediately into the selecting unit)
This definitely sounds like a bug. Having three different outcomes from basically the same action (moving a pilot from one unit to another) seems unusual, to put it mildly.