Thank you for your post.
I have not encountered this issue, so I'll need more information from the "4 times" where this has occurred.
Do you notice any commonality between the four instances? That is, you mentioned this has occurred with four different files. Do the files have any common relationships?
In the layout where this occurs, have you tried creating a new layout?
The next time this occurs, write down exactly what the customer was doing. If the user inadvertently performed Select All prior to changing a field, this would affect the styling on all objects.
Any other information you can provide may be helpful in narrowing down possible causes.
This is not a thing can can happen in browse mode so I have been the person this has happened to since only I am in Layout mode. This occurred in completely unrelated customers files.
In the most recent example I went into Layout mode, clicked a field and clicked to copy the attributes using the icon to copy attributes on the inspector. The next moment 2/3 of the fields are all messed up. The way they are messed up is the same way as if I changed theme and the fields default based on that theme. It is as if the theme was reverted. I have to then go apply theming to the layout again.
I have not tried re-creating but an terrified of using 13 on my databases. They are large databases with hundreds of layouts and rebuilding from scratch is only an option when I choose to leave Filemaker to another database platform. I can post a after picture but that is easy to fake since I can take any layout, apply a new theme and watch it go bad until the needed specific thumbing is applied.
The only commonality is that it occurs when changing an single objects theme. It is not an issue of multi selection because what it reverts to is not all the same but different object types have different attributes after the error occurs. All the files however are not created in 13 but upgrades from Filemaker back to 5.
I just did a quick test in WIndows 7 and could not replicate. I have a lot of "throw away" files, so I'll try this off and on with different files and layouts for a while over the next few days and see what happens.
But one "fall back" that you have to protect yourself is to make sure that your preferences are not set to auto-save layout changes. Then, whenever you do an action that will risk such an effect, you can save your layout changes just before you do that, then if this change happens, you can return briefly to browse mode without saving the layout changes to protect your layout from the unexpected and unwelcome change.
I change layout every day all day in filemaker and have been using Filemaker 13 since it was official and seen this only 4 times so I find it might be hard to reproduce on demand.
I do not auto save layouts so you now bring up a point I do not remember when the change occurs. In the time it happened today and I had to rebuilt a layout was copying attributes but the reverting may have been seen when I went out of layout mode to browse. I will take special note when the next time since I know I would not have save a bad layout and it caught me all 4 times now. I will see if it occurs on save and not before the save.
I have had this happen again and again and now even in a Brand New database created solely in Filemaker 13. The time it occurred in my new file was when applying attributes to a field all the fields reverted to their default theme settings.
The other time in my main project I was pasting a tab object with all its elements onto a layout. Both layouts had the same theme and earlier that day were duplicates of each other. When I pasted the elements all the other elements reverted to their default theme state.
This occurs to items that have a style applied. Fortunately I do not use too many style yet and work with object defaults. Using the defaults on everything is the only safe procedure.
If you have not seen this happen yet in your Filemaker 13. You do not work enough with layouts and themes beyond the default object themes. in 5 different database this has occurred over a dozen times. I pray every time I paste and object or change that thaw layout is kept in tact. And Yes I do use a custom theme with my own name mostly. However yesterdays reverting was a BRAND NEW database with the River touch theme proving it is not my handiwork that is causing this issue.