Viewing Property Sheet properties in the editor usually erases any values you've put in

[assaultdoor]

I'm running Vassal 3.6.9 on MacOS.

If you create a Property Sheet, put values on it, and then open and close the Property Sheet properties window from Current Traits, all the values you typed into the Property Sheet are gone, usually.

1. Create a piece with a Property Sheet.
2. Add some properties to the Property Sheet.
3. Click the preview window on the left, press Ctrl+P, and type values into those properties.
4. Close that Property Sheet values window.
5. Reopen the Property Sheet values window using Ctrl+P again.
   Expected result: the stuff you typed in is still there.
   Result: It is. Yay!

Repeat steps 1-5 above.
6) Open the Property Sheet properties window by double-clicking the Property Sheet in the list of Current Traits.
7) Close the Property Sheet properties window via the close window button or the Okay button.
8) Close the Property Sheet values window.
9) Reopen the Property Sheet values window with the list of values using Ctrl+P.
Expected result: the stuff you typed in is still there.
Result: It is. Yay!

Repeat steps 1-4 above.
5) Open the Property Sheet properties window by double-clicking the Property Sheet in the list of Current Traits.
6) Close the Property Sheet properties window via the Cancel button or the escape key.
7) Reopen the Property Sheet values window with the list of values using Ctrl+P.
Expected result: the stuff you typed in is still there.
Result: It is. Yay!

All good so far. Here's where things go off the rails, and I don't think it should be that unusual of an event.

Repeat steps 1-4 above.
5) Open the Property Sheet properties window by double-clicking the Property Sheet in the list of Current Traits.
6) Close the Property Sheet properties window via the close window button or the Okay button.
7) Reopen the Property Sheet values window using Ctrl+P again.
Expected result: the stuff you typed in is still there.
Result: It is not. All values are empty.

This makes it very annoying, although not actually impossible, to edit or add properties to the property sheet.

[Cattlesquat]

I've added PR #11974 to possibly address the issue. @assaultdoor if you wanted to give the build a try for me that would be most helpful (vassalengine.org/builds and it will be the 11974 build, appearing about 20 minutes after I post this). Also let me know what happens if you remove properties from an already-set-up-with-values PropertySheet-- best is "still works perfectly", next best is "values shift to wrong properties", worst is "crash", haha

[assaultdoor]

It is "values shift to wrong properties." Or, I guess, "properties shift to wrong values." The property name is deleted, but the value is still there. If I insert a property in the middle, the property name is added but a blank space for a property value is only added at the bottom of the list.

[Cattlesquat]

Hmmm... I guess that's probably better than the current behavior? But I'm going to maybe bump this one to the next milestone and see if I can think of something better (that doesn't involve major cranial surgery ... PropertySheet was unfortunately written long ago and is a bit cryptic and old fashioned in its ways...)