Hello Jarek, 

This mapper is no longer active with our team, but I can respond on her behalf. 

The most likely reason that the tag was removed from this location is that it was placed on an intersect node with Cartwright Ave - our team member may have thought that this was incorrect since there is a valid crossing on that same road immediately to the west, very close by.  (It does not appear that her edit was caused by a tool suggestion). 

If your original edit was meant to indicate no crossing across Dufferin Street here, perhaps we can add a new node just to the north and/or south of node https://www.openstreetmap.org/node/432744847 to add the crossing=no tag to, that way it will more directly show that it is for Dufferin Street. 

Please let me know if this edit would be acceptable. 

Thanks, VLD157