Can a tab masquerade as a space in a unicode string?

I have some code that is intended to remove spaces from some data I’m ingesting from a group of shapefiles into a number of feature classes. The malformed data consistently looks like this:

ABC12345678 90

and I want to make it look like:

ABC1234567890

Simple, right? So the code block goes:

with arcpy.da.UpdateCursor(fc, 'FIELD') as cursor:
    for rows in cursor:
        if rows:
            firstValue = rows
            secondValue = firstValue.replace(' ', '')
            rows = secondValue[:13] #this is because some rows have more than 13 characters
            cursor.updateRow(rows)

I’ve inserted print statements and it is getting into the loop, but the .replace method is not doing anything.

I’ve also tried swapping out .replace() with

secondValue = (firstValue[:11] + firstValue[12:])

and no dice there either.

The print statements show:

[u'ABC12345678 90']

through the entire loop – neither replace() nor concatenation is having any effect.

Is it possible that this is not actually a space character? Could this be a tab value or something which is causing this code to fail?