Unexpected behavior with `set -a var "string"`

[warptozero]

Expected behavior in an interactive session:

> set cmd one two
> set -a cmd "three"
> set --show cmd
$cmd: set in global scope, unexported, with 3 elements
$cmd[1]: |one|
$cmd[2]: |two|
$cmd[3]: |three|

Observed behavior in an interactive session with pisces installed:

> set cmd one two
> set -a cmd "three"
> set --show cmd
$cmd: set in global scope, unexported, with 2 elements
$cmd[1]: |set -a cmd |
$cmd[2]: |three|

The command input was set -a cmd "three[enter]. When the closing" is also typed as in set -a cmd "three"[enter] the output is:

$cmd: set in global scope, unexported, with 2 elements
$cmd[1]: |set -a cmd "three"|
$cmd[2]: |three|

However when the complete line set -a cmd "three" is pasted in it works correctly.

I can reproduce this consistently on my system with fish version 3.7.1 in a fresh config directory with only jorgebucaran/fisher and laughedelic/pisces installed.