The entropy call with Melinder fluids changes with multiple calls. A simple test code:

from CoolProp.CoolProp import PropsSI

print PropsSI('S', 'T', 313.15, 'P', 100000., 'INCOMP::MEA[0.6]')
print PropsSI('S', 'T', 313.15, 'P', 100000., 'INCOMP::MEA[0.6]')
print PropsSI('S', 'T', 313.15, 'P', 100000., 'INCOMP::MEA[0.6]')

returns:
227508.367363
215363.646742
191074.205501

I have done a bit more testing:
-Occurs for other Melinder fluid mixtures
-Does not occur for single component incompressible fluids
-Does not occur for other property calls
-Does not appear to depend on the input values

I just upgraded to the latest version. I don't think this problem occurred before upgrade (4.?), but I can't be 100% sure.