ShowSection / ShowWYSIWYG droplet doesn't work

[Ruud]

Typically, if a droplet doesn't work and still displays the [[dropletname]], something else is wrong and the dropletcode is never executed.
Use the error_reporting setting to find out if something else is wrong.

[Argos]

I use the ShowSection / ShowWYSIWYG droplet a lot on many sites. Yesterday i wanted to use it on a site where I didn't use it before. To my surprise it just showed the droplet code, instead of the wanted output.

Some other droplets on that site do work however, for example the Lorem, Children and SearchBox droplets. But the LoginBox droplet also does not work. Apperently the problem is not so much in the droplet module itself, but in the code of some droplets.

The funny thing is: the faulty droplets do work on other sites  on the same server, so the PHP settings should be fine I guess. I suspect it has something to do with the WB version. This particular site has BW 2.8.1. I'm reluctant to upgrade because I think I did some modifications on the core when I created the site, but I forgot to document them somewhere, so I am not sure what will possibly break when I upgrade.

Does anyone know what could be the problem (and possible solution) for this situation, so that it's not necessary to upgrade WB?