
The Shanghainese transcription of 望 has an m initial, but in the word 希望 it is pronounced with the 文读 pronunciation with a "w" initial. This is also the case in the word 失望, but I don't know if this is true in every compound word with 望?

The transliteration of 望 is not correct. It should be pronounced with a "w" initial.
You can find some examples here :
http://dict.cn/shh/index.php?q=%E5%B8%8C%E6%9C%9B
Tibzimin
Sken-d akk ticraḍTibdarin
Aḍris n tefyar
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Aɣmis
Tafyirt-a tettwarna deg tazwara d tasuqqilt n tefyirt # 333542
yerna-t fucongcong, 3 Ctembeṛ 2010
icudd-itt fucongcong, 3 Ctembeṛ 2010