SPI decoder on DSOX2000 series oscilloscopes

[ABH]

My DSO-X 2002A oscilloscope has the DSO, EMBD (and other) options.
I somehow managed to decode a 3-wire SPI bus using SCLK on the external (trigger) input, MOSI on channel 2 and MISO on channel 1.
CS was set to "Clock Timeout". I had the decoding working on screen and in the Lister.
When I had this working I observed, that the Acquisition Rate was only half of what it used to be (for the same time span).
This was quite surprising, because in another setup where I did 2-wire SPI decoding I had SCLK on channel 1 and still had both channels stored in memory with normal Acquisition Rate.
Therefore I left this 3-wire decode mode, that I accidentally had managed to set up, and went back to 2-wire SPI decoding.
I have now tried for hours to get the 3-wire decode mode back but this seems impossible. Having SCLK on EXT input works fine and CS set to "Clock Timeout" also works fine, but I cannot select another channel for MISO. If MOSI is set up on channel 1, then it "merges" MOSI and MISO on channel 1 and the same happens if I change MOSI channel to 2, then it merges both chanels in the decoder to channel 2. The channel display on the screen correctly shows what is connected to the channels, i.e. both MOSI and MISO are shown correctly and stored in memory. It is only the decoder that refuses to decode more than the MOSI channel.
 
According to the documentation for the EMBD option it is not possible to decode 3-wire SPI, -this requires a 4-channel model. It just annoys me that I actually had this working.
Does anyone have experience with 3-wire SPI decoding on a dual-channel model?