That is normal. SSDs don't work well with the rockbox disk driver.
To add to this, and based on personal experience:
SSDs will work with Rockbox, but they won't have the benefits of SSDs. My iPod Video
and iriver H320, both using PATA SSDs (Supra Talent 128GB SSD in the Video, Kingspec
128GB SSD in the H320). While both function quite well with Rockbox installed, there still
is contending with a lot of the same problems of slow, platter HDDs: "spinup", "spindown",
slow read access. I'm glad I have a storage medium with good space and no moving parts,
but Rockbox's disk driver is still tuned for older HDDs and thus all of its timing functions are
not optimized to use the benfits of an SSD, and it shows.
Our old friend Mr. Someone needs to step up and get the disk driver code up to spec to
take advantage of the benefits of SSDs. This will make using them a better way to go over
the old CF card substitution; CF cards are getting pricey and SD-to-CF adapters are not
a super viable alternative for that.