With apologies if this has already been mentioned. (I don't feel like searching the mailing list archives right now, and I haven't checked the test suite.) I just thought it was funny / interesting. ;-)
{ using GPC 20070904 / GCC 3.4.4 via DJGPP
(gpc.info) :
"GPC's default behaviour is (like BP) not to allow mixed comments"
... except that it allows it by ignoring it, not reporting an error (which is what was implied, or so I thought!) }
{ $ extended-pascal} { says "Hello, mixed!" } { $ standard-pascal} { says "Hello, mixed!" } {GPC default} { says "Hello" } {FPC default} { says "Hello" }
program comment(output); begin write('Hello'); { *) write(', mixed!'); (* } writeln; end.