OMX Video capture Skip mask

I have a OMX component chain that goes something like Cap -> dei -> encode.  My input is a PAL camera that does 576i @50FPS. The trouble is that I would like to implement the skip mask in the capture component. I set it to the default sCapSkipFrames.frameSkipMask = 0x2AAAAAAA; which should equate to skip every other frame. This works, sort of. When it works, it works perfectly; there are times when it will not capture any frames at all. If I disable the skip mask then everything works like a charm. Therefore I must ask if there is a different skip mask so that I can get 25fps from my 50fps input.