words with the apostrophe on the IPhone5s I OS7

HI all. I've picked up something weird. voiceover pronounce words containing the apostrophe symbol in a weird way. for example: you're is pronounced you re, don't is pronounced don t, can't is pronounced can t etc. I find it quite irritating and confusing. I'm so used to jaws on my computer pronouncing words with an apostrophe correctly. I have tried all the voices: American English, british English, irish English, south African English and Australian English. I have made sure that the punctuation setting on the rotor is set to none. Has anybody experienced this? Many thanks for any help.