Was defo a LCR I saw that time. I've seen Kat's RR thread and on the Polished Bliss site, never seen it in person as such tho.
The standard DV and the Forge 007p are recirculating dump valves (or diverter valves). They work by releasing pressure back into the TIP rather than out to the atmosphere (hence very little noise). The Split R is part recirculating, part atmospheric, so some of the air gets dumped out to the atmosphere, hence there's a bit more of the classic dump valve sound. The
problem is that the ECU in these engines doesn't expect to see boost air dumped to atmosphere so sometimes it will think there's a boost leak and run the engine in limp home mode.
I gather there's an adjuster on the Split R which lets you set how much air is dumped out to the atmosphere, most people on here seem to suggest setting it to dump all the air back into the TIP, you'd need to have a look on the Forge website or search the mk1 LCR forum to find out
how to do that tho. Even with the valve in fully recirc mode some folks have still reported problems but if your car is happy with the valve then there's nothing to worry about