Developing a working theory to reconcile the Mystery of the two Mary Ebbotts

In the 1841 Census in Cornwall, there are two Mary Ebbott’s born about 1786 in the county of Cornwall. When searching on the web, I noticed that these two Mary’s are often interchangeable and both often assigned to my ancestor Mary Ebbott (nee Ferrett). 

This is further complicated by both of these Mary’s staying with families who are directly related to my ancestors. 
In household 1 Philip Ebbott is the eldest male in the household. Mary in this household would be Philip’s wife, and therefore my ancestor. This is corroborated by the 1851 census, where both are listed as husband and wife.
(Ancestry.com, "1841 England Census," database online, Ancestry.com Operations Inc, Ancestry.com.  (www.ancestry.com.au : accessed 1 Jan 2010), entry for Philip & Mary Ebbott & family, Tressmeer, line 19 - 24, Parish: Tresmeer; County: Cornwall; PRO HO107/134/14/: ; Page: 7.) 

In household 2 John Bone is the eldest male of the household. John is the father-in-law of Sarah Ebbott, Mary Ebbott (nee Ferrett)’s daughter. It is possible that Mary could have been visiting Sarah’s in-laws on the night of the census. John Bone’s wife Grace died two days before the census and this could have been the reason for the visit. I can find no further record of this second Mary Ebbott in the 1851 census or death between 1841 and 1851. 
(Ancestry.com, "1841 England Census," database online, Ancestry.com Operations Inc, Ancestry.com.  (www.ancestry.com.au : accessed 1 Jan 2010), entry for John Bone & family & Mary Ebbott, Treludick, Lines 10 - 14 & line 22, Civil Parish: Egloskerry; County: Cornwall; PRO HO107/134/7; Page: 10.)

Working Theory 
Both Mary Ebbott’s in the 1841 census are the same person who was registered in two places. She may have been staying the night of the census with relatives (John Bone), and was included on the household census. And at the same time Mary’s husband, Philip Ebbott, not following instructions to the letter, may have included her in the household as this is where she lived. 
If the head of household was literate then they would fill out the census for the family. This could mean that husband, Philip Ebbott filled the census out as soon as he got it and/or it sat around waiting to be picked up, in the meantime his wife may have gone visiting to John Bone's either for the day or overnight and as a consequence was recorded as being at the Bone's residence as well. The residences being only 3 miles apart this would be have been quite plausible.