What version of WinSCP are you using?
I get:
bla.php4: "PHP4 File"
bla.php5: "PHP5 File"
asdf.php5: "PHP5 File"
bla.asdfg: "ASDFG File"

Anyway the value of "Type" column is generated by operating system. What version of Windows are you using?

Also to sort by an extension you should better click the "Ext" path of the "Name" column.

If you have a file:

bla.php4 the "Type" column says PHP
bla.php5 says PHP
asdf.php5 says PHP
bla.asdfg says ASD

Does affect sorting by type to wrong results, gets sorted like that, which is wrong:

asdf.php5
bla.php4
asdf.php5

Thanks for the great product! Keep your very good work!