This can happen- the contact point of the flash may be closing too soon.
Kiev RF use a single pin which acts as a simple switch to acomplish flash synchronisation. It's capable of X synch only, so there's no adjustable 'delays'. So for flash bulbs, only 1/25 can be used.
This simple pin contact is also reason why Kiev flash contacts remain closed until the shutter is rewound. When left in its fired state, the flash can fire spontaneously. The pin remains in a constant position, keeping the circuit alive, once actuated. Also, this is reason why a charged flash will also fire when the Kiev shutter is rewound when the flash is connected.
The pin closes the circuit by striking on the metal parts of the roller blind (or the shutter crate?) as the shutter travels. One of this pin's ends is actuated by the moving shutter itself. If this part is deformed, the synch circuit can close, and fire the flash, before the shutter blinds can fully open at 1/25 sec. Since you're seeing the upper part of the frame unexposed (this part would be at the bottom of the camera's film gate), the synch circuit is actually firing prematurely. Part of the first blind is still covering the gate when the flash fires.
The only way to remedy this is to disassemble the shutter and reshape the contact pin (it's actually a very tiny triangular piece of metal) so that it makes contact just at the right moment. According to Maizenberg, the pin can be accessed by simply removing the shutter cover- I don't really know how this can be done this way since I found it hard to reach the contact pin with the cover removed.
I would say that adjusting the contact pin is really tricky to do. Finding how much to bend or twist it so that it times correctly with the shutter is largely a matter of trial and error.
It seems that correctly synched flash are part of the QC problems of the Kiev cameras. My 1980 4a did this too.
Jay
