Solution works locally (v23.06), fails on test runner

I’m not sure if this is due to some fix since version 23.01.01, or something more subtle. The following code for the Series exercise passes all tests when I run it locally:

: slices \ s n -- a[s]
    >r [1] s:/ ( "" a:join a:push ) a:new r> 1 a:reduce+ ( "" = not ) a:filter

But it throws an exception on the test runner:

We received the following error when we ran your code:

Exception: Expected Array but got Number: at line 4 byte 72 in series-tests.8th ← user:slices: task REPL

Inserting .s in various places (in the code editor) seems to show that the stack is correct at the time of the a:reduce+ word. And the placing .s after a:reduce+ doesn’t show the stack, so that must be where the exception is thrown. That makes me think it’s a bug in 8th itself, perhaps, but maybe I’m missing something.