Containers and themes

[redcat13]

I seem to be having a relatively common problem with containers and the application of themes by visio when I don't want the theme applied. I have created a custom theme and am creating simple containers - some are two layers deep. Nothing complex. I have read articles/blogs about unapplying the theme and setting properties in the design tab - which I have done. However, I am still having the problem whereby as I am working, visio will decide to change some, not all of the containers to what seems to be a "random" color. This color is not one in my custom theme.

The only way I can get back to where I want is to manually modify or in some instances delete and add again.

Does anyone have other ideas what might be the route cause of this? It is very irritating and really is something visio should handle very simply.