HowTo use lwip debug feature?

Does anybody know how to enable the lwip debug feature?

In the lwipopts.h file I set LWIP_DEBUG to 1 and all variables below to (DBG_ON | DBG_TYPES_ON). Everything else is left as is.

Even though I clean the project and recompile it the lwip debug messages are not shown.

What else can I do?

plz help

--wolf