Use on'yomi instead, for some godan and ichidan verbs?

There was a discussion on here recently about how to know when to use either on'yomi or kun'yomi...
http://japaneseclass.jp/bulletin/thread/778

...and I gave this link to a page that answers this question almost perfectly:
http://lingwiki.com/index.php?title=On_vs._Kun_readings

But, one thing this link effectively says is that all godan and ichidan verb kanji are read using their kun'yomi. Today I got a practice question wrong probably because I took this too literally.

What that page says is not actually wrong, but there is one small caveat to it:
- Single kanji + -suru/-zuru irregular verbs kanji are usually (always?) read using their on'yomi.

Now this is fine so far, as this should have nothing to do with godan and ichidan verbs, however...

- The -する ending has an alternate -す version for single kanji suru verbs:
愛する【あいする】= single kanji -suru verb, kanji reading is on'yomi.
→ 愛す【あいす】= godan verb ending in -su (kanji reading is still the same).

- Apparently this can be done with -ずる too!
禁ずる【きんずる】= single kanji -zuru verb.
→ 禁ず【きんず】= godan verb ending in -zu ! (kanji only has on'yomi)
(e.g. 立ち入りを禁ず = No entry. / Keep out.)

- The -ずる ending has an alternative, much more common -じる ending:
感ずる【かんずる】= single kanji -zuru verb, kanji reading is on'yomi.
→ 感じる【かんじる】= ichidan verb, -jiru (kanji reading is still the same).

The word in the practice question I got wrong was 通じる.

I glanced at the word, thought it must be an ichidan verb, so I read the kanji as kun'yomi 'とう'...
I thought for a second とうじる sounded wrong, and かよじる sounded worse, then without thinking properly anymore about the kanji, I just thought 'traffic' or 'commute'...
So I clicked a different answer which looked more correct, but still looked wrong. Was wrong. -_-

通じる【つうじる】is one of those -jiru ichidan verbs (an alternative of its -zuru verb form) therefore on'yomi reading...

I thought this was interesting anyway, and it doesn't seem like something that usually gets mentioned. ^^