st -e neomutt working fine, the way I usually fire up neomutt. Worked fine on all previous versions, including 20171013.

Running st -e neomutt or any other equivalent, such as xterm -e neomutt (happens on xterm too).
Note that opening up a terminal first and running neomutt from the shell does not show this issue. I'm using that as a temporary workaround for now.
System: Linux 4.14.4-1-ARCH (x86_64)
ncurses: ncurses 6.0.20170902 (compiled with 6.0)
libidn: 1.33 (compiled with 1.33)
hcache backends: gdbm
Compiler:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/7.2.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --enable-libmpx --with-system-zlib --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib --disable-werror --enable-checking=release --enable-default-pie --enable-default-ssp
Thread model: posix
gcc version 7.2.1 20171128 (GCC)
Configure options: '--prefix=/usr' '--sysconfdir=/etc' '--enable-debug' '--enable-gpgme' '--enable-lua' '--enable-notmuch' '--with-gss=/usr' '--with-ssl=/usr' '--with-sasl' '--with-curses=/usr' '--with-idn' '--with-gdbm' 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt' 'LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now' 'CPPFLAGS=-D_FORTIFY_SOURCE=2'
Compilation CFLAGS: -Wall -pedantic -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt -fno-delete-null-pointer-checks
Default options:
+attach_headers_color +compose_to_sender +compress +cond_date +debug
+encrypt_to_self +forgotten_attachments +forwref +ifdef +imap +index_color
+initials +limit_current_thread +multiple_fcc +nested_if +new_mail +nntp +pop
+progress +quasi_delete +regcomp +reply_with_xorig +sensible_browser +sidebar
+skip_quoted +smtp +status_color +timeout +tls_sni +trash
Compile options:
+bkgdset +color +curs_set +fcntl -flock -fmemopen +futimens +getaddrinfo
-gnutls +gpgme +gss +hcache -homespool +idn -locales_hack +lua +meta
-mixmaster +nls +notmuch +openssl +pgp +resizeterm +sasl +smime +start_color
+sun_attachment +typeahead
MAILPATH="/var/mail"
PKGDATADIR="/usr/share/neomutt"
SENDMAIL="/usr/sbin/sendmail"
SYSCONFDIR="/etc"
In case the problem isn't obvious - neomutt appears to just use 80x60 on the top left, instead of using most of the terminal window as usual.
This is on Awesome, a tiling window manager, in a mode where all windows are maximised at all times. If the window is resized, neomutt does fix itself.
This is my fault. I put in a line of code to stop macros being eaten on startup.
I'll revert my change.
(Neo)Mutt's keyboard/macro handling needs a big overhaul.
Great - thanks for taking this on so quickly. I was fearing it would be a tricky issue to reproduce or nail down :)