I was checking a mezuzah yesterday, in the word ירבו the ב' has a little tiny Chut hasara that seems to connect to the roof giving it a possible appearance of a ם. Although I must say it is not so noticeable by the naked eye, however I did catch it without a magnifier glass. The Mezuzah is 10 cm big, to give you an idea of how small it would be.
This was the Rabbi"s answer;
צריך הבחנת תינוק, ע"י כיסוי האות וי"ו שלאחריו
Knesset Israel, Beverlywood Los Angeles