Good thoughts; but no dice yet.
I checked various settings in UE; and "Trim Trailing Spaces on Save" was Off (as it should be for this I suppose).
But, "Allow low ASCII values t be entered" was off. I changed it to on.
"Allow editing of text files with HEX 00's without converting them to spaces" was also off. I changed it to on.
But the same thing happens.
Basically, UE only decodes the first 5 bytes. When I look closer at those bytes and the "working" zip in hex mode; I see that the sixth, seventh and eighth bytes happen to be 00 (null) in the working zip produced by Notepad++.
I guess that despite my changing UE options that specify hows to handle 00's, UE's Base64 Decode is for some reason stopping the decode when it decodes a null value.
There may be other options I still need to set correctly. But there is no help on the new Base64 Decoding that I can find, that might explain what I need to do.
Perhaps tomorrow, if someone hasn't chimed in that knows what to do, I will email UE tech support about this.