See Apparently misbehaving PDF-Xchange Columns Extension
I did report the issue to Tracker Software and got the following reply which I can't say I really understand:
The Column and Properties sheet handlers both accomplish the same thing, but one is the "legacy" version of the handler. With regards to Windows explorer, the "Column handler" is for windows Vista and Up, while the "Properties sheet handler" is for everything prior. We still offer both however as some 3rd party applications make use of one or the other, and we cannot discern which they will need. All that this accomplishes is offering some additional information in the columns of these applications, such as the PDF specification of the file.
I will forward this report to the relevant Development team members so that they can look into it.
There were no further replies in the thread so I don't know if anyone actually looked into the matter.
I've been perfectly happy with the shell extension indicated in my referenced post disabled,