Scalar Function produces different results for a string and the same value as a variable

Question

I am working on a TitleCase Function and have found an infuriating issue that I can not figure out.

This select dbo.lf_titlecase('30600 N. Pima Rd. unit 16','street')

Results in 30600 N Pima Rd Unit 16

But this

select customer_no
    ,address_no
    ,street1
    ,dbo.lf_titlecase(street1,'street') "upd_street1"
from t_address a
where 
customer_no = 174242

Spits out 30600 N Pima Rd unit 16

In the first case I am directly copying the string from T_ADDRESS.

This SELECT DIFFERENCE ((SELECT street1 FROM T_ADDRESS WHERE address_no = 83212), '30600 N. Pima Rd. Lot 16') Gives me 4 so they should be the same.

I must be missing something!

I've ensured the function is Scalar and should be used in this way. If I change the address first to 30600 N. Pima Rd Unit 16 then I get the correct output. So it seems the . is causing the issue but still that period does not cause a problem when using the function with a hardcoded string.

Here is the main part of the function:

 BEGIN
    DECLARE 
      @StrOut NVARCHAR(1024),
      @CurrentPosition INT,
      @NextSpace INT,
      @CurrentWord NVARCHAR(1024),
      @StrLen INT,
      @LastWord BIT
    SET @StrIn = case when @StrIn = '' then null else rtrim(@strIn) end
    SET @NextSpace = 1
    SET @CurrentPosition = 1
    SET @StrOut = ''
    SET @StrLen = LEN(@StrIn)
    SET @LastWord = 0

    WHILE @LastWord = 0
      BEGIN 
        SET @NextSpace = CHARINDEX(' ',isnull(@StrIn,' '), @CurrentPosition+ 1)
        IF  @NextSpace = 0 -- no more spaces found
          BEGIN
             SET @NextSpace = @StrLen
             SET @LastWord = 1
          END
        SET @CurrentWord = Upper(SUBSTRING(@StrIn, @CurrentPosition, 1)) 
        SET @CurrentWord = @CurrentWord + Lower(SUBSTRING(@StrIn, @CurrentPosition+1, @NextSpace - @CurrentPosition))
        --SET @CurrentWord = case 
                            --when @NextSpace = 0 and len(@CurrentWord) = 1
                            --then @CurrentWord + SUBSTRING(@StrIn, @CurrentPosition+1, @NextSpace - @CurrentPosition)
                            --else @CurrentWord + Lower(SUBSTRING(@StrIn, @CurrentPosition+1, @NextSpace - @CurrentPosition))
                            --end   
        SET @StrOut = @StrOut  + @CurrentWord
        SET @CurrentPosition = @NextSpace + 1
      END
    IF CHARINDEX(',',@StrOut)> 0 and @type = 'city' 
      BEGIN
        SET @StrOut = replace(@strout,',','')
      END

T_ADDRESS.street1 is varchar(64)