I agree with you in entirety. It is not uncommon to find such problems in respect of other English words and other languages as well. Most Tanzanians are influenced by their Kiswahili accent as they import it to their spoken English. This problem is a common phenomenon in language studies and learning among non-native speakers who learn another language. Therefore, you will find it not only with Tanzanians who speak English but also with non-native swahili speakers who attempt to speak Kiswahili. Consider a mzungu speaking kiswahili for instance. Or, a Nigerian speaking English. etc. However, this problem tends to reduce with those who have travelled outside their mother tongue areas to live among the native speakers or people with a different, but better, accent. I had a friend of mine from Kenya (a kamba) when I was abroad for further studies. She could not pronounce "v" or "d" in some words. She would for instance say "fondacom" for vodacom, "afond" for afford etc. Therefore, one learns a better way when one finds that others cannot understand him/her or they frown when he/she promounces certain words. I am not spared. I used to pronounce the word gift with a "dg" instead of "gi" untill my friend whose name is Gift could not tolerate it anymore and told me.
