I would expect that what you describe is correct - if you are talking about sheet2 being called "January" and sheet3 being called "February" then if you copy
=JanuaryA1+1 from sheet2 to sheet3 it would remain = JanuaryA1+1
if you copy
=A1+1 from sheet2 to sheet3 it would remain =A1+1 when moved to the next sheet, in essence changing the sheet reference.

So if you copy and paste across sheets with a sheet reference typed in it stays the same.

Unless you are talking about in one workbook where you had some sort of macro set up to deal with the sheet renaming.