I've had a strange phenomenon that I haven't been able to resolve totally. I use a theme other than the default theme for my blog site. However, after upgrading WordPress, the theme doesn't stick. That is, it keeps defaulting back to the wordpress default theme. If I go in and select my chosen theme, it works until, I think, I have logged out of WordPress. At least if I check it later, it has dropped to default. The only way I have been able to get it to keep my chosen theme, is to copy all those files into the default theme directory /wp-content/themes/default dumping the original default files. Then it works fine.
Where in the code have I gone wrong. Certainly not in the configuration file as I copied over my originally working version to make sure my settings would remain.
Any advice would be helpful. It is probably obvious, I am not a strong php programmer though I can understand it if I can find it!