Pitch bender changes pitch randomly

[Alcala]

Hi,

I play a Roland Juno-DS88, a versatile keyboard that works pretty well overall; but suddenly the pitch bender started doing funny things: when I do pitch bends, the sound doesn't quite go back to its original tune. It stays about a half tone higher, then slowly falls down to the correct note—what creates a bizarre effect as everything you put in the solo is out of tune—. No clue why is this happening. Please, help. I have got a busy agenda and I can't work comfortably until i get this issue solved.

Many thanks.
Ernesto