Different Duration Format/s (Separators)

[dec]

i am getting different duration separator formats in different places

previously, i have a note (i wrote for future reference, like now) that i got _ in Field Name, and : in Title, and just this second (no pun intended), i got no separators at all in the duration string

one obvious question that raises is if the duration strring format depends on the individual data, although, to date, it has been very consistent

otherwise what causes this issue and what is the fix?

UPDATE

1. i tested a FN Covert incl Duration, and in the Preview it showed the duration correctly formatted (with colons) so i thinking that the previous was just a formatting glitch and it actually does it correctly, BUT ....
2. after i rann the Copnvert on a few files, it actually added Duration UNFORMATTED ie NOT the same as teh Preview.

so now i wil add screen shots.

UPDATE
have again confirmed different Length formatting when using in FN and Title. and now, in addition, a THIRD varitaion - if you use Length in a Tag-Tag for FN, you get no formatting at all

here are some more confirming screenshots ...

this should now be moved to Bugs.

[poster]

No bug.
Your screenshots show 3 different cases for the converter:
1 x Tag->Tag for the TITLE field
1 x Tag->Filename
1 x Tag->Tag for the YEAR field

For the TITLE and YEAR fields, the colon is displayed in the result of the format string.
When formatting the FILENAME, an underscore is displayed instead of a colon.

The colon is an invalid character in file names on Windows and must not be used. Mp3Tag will help you in this case and replace the colon with an underscore.
https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file

[dec]

hi

i am aware that colon cannot be used in windows file names. i have been programming BEFORE there was Windows.

1. that is half my point - the Length format SHOULD HAVE BEEN CONSISTENT across all Fields.

2. the other half of my point is that we are getting different format results using the same field, Length, when inserted in different ways, as shown, somethimes with NO formtting, sometimes with an Underscore

3. the THIRD issue is that when there is actually no formatting, Preview shows (colon) formatting

[ohrenkino]

@dec

the Length format SHOULD HAVE BEEN CONSISTENT across all Fields

The length format is consistent across all fields. It is not consistent across all properties. The filename is a property defined by the underlying OS which MP3tag cannot influence.
But you said yourself that you are

@dec

aware that colon cannot be used in windows file names

so I wonder what all the fuzz is about.
In all the other examples that you provided (YEAR, TITLE) the output for _LENGTH was with a colon, so probably as expected by you.
As the filename and its restrictions is not under the control of MP3tag but defined by Microsoft, I find it a nice feature that MP3tag takes care not to produce an invalid filename just because the user did not pay attention.