Not really debugged this at all yet; I've merely noticed it in my modified version of the standard template, and then restore the default one to confirm it wasn't just me.
If a file name includes numbers, and you rename it to insert a "$" before those numbers, the $ and some numbers are deleted from the name.
The specific example I found was attempting to rename the file name "SCS_A01_10039.CSV" to "SCS_A01_$10039.CSV".
The resulting file name became: "SCS_A01_039.CSV". That is, the "$10" was deleted from the new name.
"$" works fine in other parts of the string, but before a digit 1-9, the $ and one or two digits are removed.