Paren expression staying permanently highlighted?

Hi, I just recently joined the beta mailing list, so sorry if this has come up before. (I did look on dejanews, but I came up empty.) I've been using version 21.0 betas for quite some time now (currently b65), and occasionally a paren expression will highlight and stay highlighted, even when the cursor is moved away. This ends up leaving chunks of garish green in my buffer. (That green is a fine color for temporary matches, but not all the time....) It doesn't always happen, and I haven't figured out what causes it. I'm seeing it at the moment running on: OSF1 turbo-01 V4.0 878 alpha and I'm pretty sure I've also seen it on Solaris. I'm not doing anything peculiar in my .emacs relating to paren matching. I don't think this happened before the 21.0 series. Anyone else seen this or am I crazy? Thanks, Reid