I've become increasingly bemused at the rate of announcer and news reader errors on Radio 4.What seems to happen is that the presenter reads from a script with errors, which trips them up.80% of the time they appear to pre-empt the error with a bit of pausing but 20% or so get through and in just the last couple of days such gems as:

"forced convection" being corrected to "forced confession""MS" being corrected to "estimated" "boiling point point"

have been blurted out. I sincerely do not believe that these people cannot read their scripts/autocues. So what's going on ? 

How are these scripts so in error and/or why do the presenters not read them through prior to reading out ?