I am sure this has been asked before, but due to this form's similarity to the causative-passive (e.g. 行かせられる), I simply cannot find anything except for some thick Japanese explanations complete with overly technical grammar terms.
I do not understand why the passive form is せられる instead of される for verbs like
発する, 罰する, 反する, and so on (so-called する verbs?). The conjugation table on Tangorin does not even list this せられる form at all.
Is the form される, e.g. 発される,
ungrammatical, unnatural, or allowed? Moreover, do these verbs have other
naughty naughty irregular conjugations that I have to look out for?
On a side note, I once read a discussion that said the alternative form of this type of verb (e.g. 罰す) is not used anymore, but I cannot locate that discussion. Would someone kindly shed light on this as well?