bug#42131: Cannot split to IMAP folders

[David A. Greene]

I am running a local dovecot instance to serve IMAP to gnus.  I have set
up splitting rules which `B q` shows work correctly:

  This message would go to home/school

However, `B r` results in:

  nnimap-request-accept-article: Writing to process: Bad file descriptor, 
*nnimap*

Dovecot shows this in the log:

  Jun 29 15:27:02 imap(dag)<14994><2s+d4T6pHsN/AAAB>: Debug: Mailbox 
work/INBOX: Mailbox opened because: SELECT
  Jun 29 15:27:02 imap(dag)<14994><2s+d4T6pHsN/AAAB>: Debug: Mailbox 
work/INBOX: Mailbox opened because: SELECT
  Jun 29 15:27:02 imap(dag)<14994><2s+d4T6pHsN/AAAB>: Debug: Mailbox 
work/INBOX: UID 2429: Opened mail because: full mail
  Jun 29 15:27:02 imap(dag)<14994><2s+d4T6pHsN/AAAB>: Debug: Mailbox mail.misc: 
Mailbox opened because: APPEND
  Jun 29 15:27:02 imap(dag)<14994><2s+d4T6pHsN/AAAB>: Info: Too many invalid 
IMAP commands. in=1444 out=626842 deleted=0 expunged=0 trashed=0 hdr_count=0 
hdr_bytes=0 body_count=1 body_bytes=622647

I'm not sure where "mail.misc" is coming from.

I am successfully able to move messages (`B m`) to other folders.

  Moving to home/school: (1933)...

Any help would be greatly appreciated!

Gnus v5.13
GNU Emacs 26.2 (build 1, x86_64-apple-darwin18.2.0, NS appkit-1671.20 Version 
10.14.3 (Build 18D109))
 of 2019-04-12