i also had this problem back when i had i flashed to metro pcs. back button would work but if i touched the physical keyboard the ghost touch would go crazy and half the keys on the keyboard wouldnt work. i eventually just started using the onscreen keyboard to avoid the problem. but my problem ended up being all software, did a full wipe and install fresh new rom and my problem was solved.
Rooted Nook Color | CM7 | 32GB Adata class 4 microSDHC SOLD
Evo 4G | CM7 | SavagedZen Kernel | 16GB sandisk class 4 microSDHC SOLD
Samsung Epic 4G Touch | rooted | Starburst v1.9
Acer Iconia Tab A500 | Rooted Stock 3.2 | Overclocked to 1.5 Ghz | 32GB Adata class 4 microSDHC
Motorola Droid | CM7 | no service but add a dock and it makes for a bad ass alarm clock