Files/folders created in Windows share are read-only... why and how to fix?

Client: MacBook Pro running 10.7.5

Server: Windows 7 desktop

I'm sharing a folder from the Windows 7 machine and mounting it on my Mac using Finder's "Connect to Server..." and an smb:// URI. I'm providing a user ID/password for an account on the Windows 7 box that has full control over the shared folder, via smb://userid:password@server/share.

The volume mounts properly on my desktop, can I can see files/folders there as expected. However:

• If I create a folder, it's read-only. I cannot create any files inside (or even see inside), rename the folder, or delete the folder. The folder has a badge: red circle with bar.
• If I create a file, it's read-only. I cannot rename it, delete it or edit it.
• If I examine File Info via Finder on any of these files or folders, under Sharing & Permissions it says "You have custom access."
• If I try to delete these files/folders, I get error code -8072. I can delete them from the command-line, but I can't otherwise manipulate them.

I've verified on the Windows box that the user ID I'm using has full control of the folder. I've also set it so Everyone has full control, with no difference.

This seems to have been a recent change in behaviour (a few weeks ago I was copying data to this drive, no problem), and it's driving me crazy because I can't figure out how to fix it.