I've seen that in Beijing Mandarin f can be pronounced as something of a final consonant when in an unstressed syllable, e.g. 豆腐 dòu fǔ = dòuff.
However, in other cases it disappears in unstressed syllables. One example is that in Beijing dialect 王府井 is pronounced as " 王五井", Wáng wǔjǐng becomes wángfǔ jǐng ( http://www.360doc.com/content/18/0123/07/1260016_724326694.shtml ).
Is this because of some kind of tone rules? Both of the "fu"s are third tones in these examples. Are there cases where both the f and the final of that syllable are pronounced in colloquial speech?