The bug that was described as fixed in the Thunderbird 115.5.2 (64 bit) Release Notes: "Apply columns to" sometimes failed to apply columns to a root folder and its descendants is still present in 115.6.0 (64-bit) - at least for me on Win10. It seems to give up part way through a large number (maybe 150-ish but I haven't counted) of folders, in that the first several (I haven't counted) folders are correct but after a point the columns are reset to the default for new folders, not the requested columns - this is regardless of whether specific columns have been applied prior to attempting to apply the requested columns - thus, after a point any previous settings revert to the default columns for new folders . Happens in Safe Mode as well. To reproduce, just run through the normal process of "Apply columns to ..", "Folder and its children..", then the account name and then the account name again to select the root folder. This is IMAP access to email accounts hosted on a domain at UK2.net Thanks for any suggestions.