Spelling pronunciation
Spelling pronunciation occurs in English when people display their literacy by using a pronunciation that more closely reflects the spelling, whether it is correct or not to do so. It is an ongoing phenomenon and can be put down to the increase in literacy over the last half century. Two common examples are mispronouncing the l in "salmon" and the t in "often". Two counter-examples would be correctly pronouncing "February" and "library", words that frequently are pronounced without the first r in each word.
Depalatalisation
Much spelling pronunciation concerns depalatalisation, usually that of s, c or t when followed by i or u as an s sound where a sh is normal. A classic example is íssue: should it be pronounced *íssyûe or palatalised as *íshûe? Clearly, the unpalatalised version *íssyûe reflects the spelling and is of greater antiquity, but is has long been the norm to say *íshûe. Even so, *íssyûe has never quite gone away, as it is perceived that resisting the urge to palatalise to the sh sound is somehow more correct. The same can be heard with tíssue, and of course there is no palatalisation in assûme and consûme: both always have -syûme: a -shûme pronunciation would sound comically uneducated. But foreigners should learn to palatalise words that normally have this pronunciation, if they are not to sound mannered. Nobody says *insyûrence for insûrance; indeed it most often sounds like *inshŏrance.
And sûre itself retains its palatalisation: AmE *shûre, BrE sůre certain = shŏre sea: it does not sound like seŵer. spêcies however has been showing signs of returning from *spêeshíz to *spêessíz or *spêessêez. Meanwhile, Cambôdia, ‘Cambodge’ in French, was for a time in the 1990s Kampuchêa in English: we can see that the -dia represents a palatalisation to a j sound that has been lost in English, and that the K- spelling was an attempt by some to restore it in the form of a ch.
Other words not normally palatalised are: assûme, dûe, ensûe, euthanâsia (-zìə), Galícìa, Parísìan (-zì-), presûme (-zyûme), pursûe, redûce and other words in -dûce, sûicide, sûit (cf. shoôt), synaesthêsia - though anasthaêsia might be (AmE both -nəs-), Tunísìa (BrE *Cheŵ-nízier) and Valéncia. Other normally palatalised words are: amnêsia (-zhə), apprêciâte, Âsia, assôciate, atrôcious, caucâsian and other words in -sian (-zhn), Chrístian (*Kríshchən) and other words in -tian (-shn), Indonêsia, milítia, negôtiate, Patrícia, Përsian, pléasure (-zh-), précious and other words in -cious, préssure (-sh-) and other words in -sure, sôciology, sôldier, substántial, Croâtia (Crô-, and other words in -tia), vísion and other words in -sion (-zhn), vítiate, volítion and other words in -tion (-shn).
Another spelling pronunciation is Colómbia for Colòmbia (= Colúmbia British, trademark), unnecessary, as there is no danger of confusion. In óften, normally *óffen, many people pronounce the t; a regular pronunciation of âi in agâin and agâinst can sometimes be heard instead of *agén and *agénst; toûr alternates with tŏur; BrE pŏor increasingly sounds like poôr, although dŏor remains unaffected.