AKG has done a rather confusing thing with their large-diaphragm studio condenser microphones for a long time now: a given model of "C 414 ..." may contain either of two very different-sounding capsule types. The older type (or since the 1970s, AKG's recreation of the CK 12 which goes by the same name) has a considerable treble boost, and is usually used for solo vocals and spot miking nowadays. The other type has much flatter response, which makes it suitable for more general applications--especially now that most people's playback equipment has more treble response than when these microphones were originally introduced.
Typically AKG offers both capsules in nearly identical-looking models with similar names and the same set of patterns and other features such as filters and attenuators built in. You have to be something of an AKG fanatic to remember which model has which category of sound--fortunately, various lists and tables have been compiled. For example, one fairly recent "generation" of the C 414 series included the C 414 B-ULS and the C 414 B-TL II, of which the former was the general-purpose (flat) model, while the latter was the vocal soloist mike / spot mike for solo instruments.
And of course you can use a "vocal mike" for more distant, live recording/stereo miking. It might even sound good a fair amount of the time, and quite good occasionally. If you often have to place your mikes farther back than you would ideally want to do, a moderate treble boost can be your friend as long as it's not too narrow ("peaky" sounding). But when you can place your mikes more or less to your liking, flatter response will give you more predictable results, all other things being equal.
P.S. about some remarks earlier in the thread: With careful enough manufacture, the two halves of a dual-diaphragm capsule can match well enough for all practical purposes. The ones from top manufacturers such as Neumann and AKG have figure-8 patterns with consistent, sharp enough nulls (which only need to be around -20 dB across the band), and the nulls are close enough to 90 degrees, and thus are completely usable for M/S or Blumlein stereo recording. This is an area of performance that commonly suffers in lower-cost microphones, though.
It is also easier to design a microphone with a dual-diaphragm capsule to have extended low-frequency response in its figure-8 setting than a microphone with a single-diaphragm figure-8 capsule--and that's a very important characteristic. I strongly prefer single-diaphragm capsules for most stereo recording, but when I use single-diaphragm figure-8s to record music that has bass in it, I nearly always boost the low frequencies in post-production.