EDIT: All other VSTis I've tested so far behave normal.
What can it be? Did I occasionally messed up something in global settings (no idea how and what EDIT: highly unlikely, as the problem happens only with Spire)?
Win 7, Studio One 2.6. 64 bit.
EDIT: was solved by upgrading to S1 v.3 Professional - I should have done this at some point anyway