probable caching bug?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

While editing a plain list yesterday I noticed what I guess was a bug in
the caching mechanism.

The list item was wrapped to several lines, and I noticed that calling
C-e while on the last line gave me "wrong-type-argument
integer-or-marker-p nil". Trying to fill the item with M-q gave me
"user-error: An element cannot be parsed line 635".

I found that adding another item with M-RET allowed me to go back up to
the previous item and fill it successfully. Later on, though, the same
error cropped up with other items, and I wasn't always able to bang it
back into shape. I was right in the middle of something and didn't have
time for extensive debugging, but here's the text I was on, and the
traceback for the wrong type argument below that:

****** Selected Quotes

- Illness is a subtle negotiation [微调] between life and death. Like
  a never-ending course in philosophy, it has taught me some of the
  meaning of life, and of death.
- One can only save the drowning when oneself is on the shore.
- Night was falling. Carrying his large leather suitcase, Zhuang
  Zhidie arrived alone at the train station. After queuing for his ticket, <--- line 365

Debugger entered--Lisp error: (wrong-type-argument integer-or-marker-p nil)
  org-element-item-parser(27819 ((27512 0 "- " nil nil nil 27681) (27681 0 "- " nil nil nil 27744) (27744 0 "- " nil nil nil 27819)) t)
  org-element--current-element(27819 element item ((27512 0 "- " nil nil nil 27681) (27681 0 "- " nil nil nil 27744) (27744 0 "- " nil nil nil 27819)))
  byte-code("BYTE CODE HERE" [element special-flag type pos org-element-use-cache org-element--cache (item table-row) (plain-list table) 0 org-element--cache-sync gethash eql objects org-element--current-element derived-mode-p org-mode nil org-element-cache-reset puthash :parent org-add-props plist-put plain-text (item plain-list) :structure :end get-text-property plist-get throw exit :contents-begin :contents-end (plain-list table) (center-block drawer dynamic-block inlinetask property-drawer quote-block special-block) (item plain-list) plain-list item property-drawer node-property table table-row org-element--cache-status data cached end struct parent value property elem-end ...] 6)
  org-element-at-point()
  org-end-of-line(nil)
  call-interactively(org-end-of-line nil nil)