Hi and Welcome to the Community!
The only way to fall back to a prior BBM version is via the Desktop Software. You should be sure you have the Desktop Software installed to your PC as well as your installed BB OS package (installed to your PC). Then, tether to the PC and launch the Desktop Software...see if it will allow you to reinstall the original version that came with your OS.
If it will not, then you will have to actually reload your OS onto your BB so as to fall back BBM to the version that came with your OS level.
But, you cannot obtain any of the versions between that original one and the most recent...there just is no way. Also, the issue you are experiencing is sadly "normal"...if you wait a few seconds (perhaps a minute), then it'll stop jumping around and act smoothly (until the next time you open it). We all are hoping that RIM is working on it and will release a fix soon.
Good luck!
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