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The sidebar patch seems to segfault randomly with the use of the unmailboxes command.
To clear up sidebar noise, I use a setup with account specific configs that are triggered by folder hooks via macros. The folder, special folders and mailboxes are set in these account specific configs after a unmailboxes * command. It works fine without the sidebar (even with the patch, but invisible sidebar). As soon as the sidebar appears, using unmailboxes/mailboxes segfaults randomly (10.6.8/Mutt 1.5.21 (2010-09-15)). Before the segfault occurs, the sidebar entries are messed up (random chars, or numbers or ?). Hitting y however shows the correct mailbox list.
I have the exact same behavior. for the issue description.
For fear of turning this into a "me too" thread, I will just add that the same happens to me too, so that it is clear this affects at least three people exactly the same way, so is obviously not an installation-specific anomaly (I think that should be enough "me toos" though...)
I am also having this issue. Apparently this used to be a problem and was fixed for mainline mutt report on trac here. I tried using the newest patch from the current maintainer but I am having the same problems with unmailboxes *, although the exact characters that show up are different.
edit: temporary workaround seems to be to just delete the unmailboxes * line. Everything works, but it ends up showing all of the mailboxes. Thankfully, it doesn't seem to duplicate mailboxes.