assertion failed in async http handler when mutating external

[y21]

Code:

import * as http from '@std/http';

let _t = 0;
http.listen(3000, async function (ctx) {
    _t++;
    ctx.respond({});
});

Output:

dash has unexpectedly panicked! this is a bug!

panicked at 'internal error: entered unreachable code', crates/dash_vm/src/dispatch.rs:1280:55
set RUST_BACKTRACE=1 to print a backtrace
dash has unexpectedly panicked! this is a bug!

panicked at 'called `Result::unwrap()` on an `Err` value: RecvError(())', crates/dash_rt_http/src/lib.rs:107:45
set RUST_BACKTRACE=1 to print a backtrace
dash has unexpectedly panicked! this is a bug!

panicked at 'assertion failed: `(left == right)`
  left: `ThreadId(1)`,
 right: `ThreadId(2)`', crates/dash_middle/src/util.rs:153:9
set RUST_BACKTRACE=1 to print a backtrace
thread panicked while panicking. aborting.
Aborted

[y21]

Doesn't seem to reproduce anymore. Odd. Closing for now.