Screen Options "Show on Screen [n] Posts" for custom post type containing digits in its name does not work

[vtowel]

1. In a plugin, write the code to register a custom post type called "all_in_1_event", or any other name that contains a digit.
2. On the manage screen for that custom post type, reveal the Screen Options.
3. Enter a new value for the "Show on Screen [n] Posts" field, something other than the default value of 20.
4. Click "Apply".
5. Reveal the Screen Options again.
6. The new value has not been saved.

It seems to be that this is because of a check that occurs in the set_screen_options() function (misc.php, line 331). The option name is not allowed to contain digits - only letters, dashes and underscores - and I don't understand why. Our custom post type does contain a digit, and it has never been a problem for us before - except for saving the Screen Options.

Related: #18559

I am using a custom post type named 'class-notes' (notice there are no digits in that label; just letters and a dash), and am experiencing the same issue in WordPress 3.2.1 and the latest nightly build of WordPress 3.3.

the glitch is confirmed here too, post type 'feed-posts', perhaps it happens for any post type with a dash in it?

See #21322 for more history. Looks like we should allow whatever sanitize_key() allows here.

#18559 was marked as a duplicate.

18323.2.patch​ uses sanitize_key().

In [22253]:

Allow numbers in screen option IDs. Fixes setting posts per page for custom post types containing 0-9. Props SergeyBiryukov. fixes #18323