Tag properties not reading consistently

I have this problem: same tag, but partial tag path results are different from full tagpath

tg is set earlier in script to the tag path.
partial script:
imode = system.tag.read(tg+".InterpolationMode").getValue()
print “tag:” ,tg," InterpolationMode = ", imode

results
tag: [Process/ignition160:default]oline/furnace/p105 profilecontrol/saturation testing/sattestindex InterpolationMode = 3
tag: oline/furnace/p105 profilecontrol/saturation testing/sattestindex InterpolationMode = 0

Do you have any idea of what I am doing wrong? the correct answer is 0 which comes from the partial tagpath.

Forgot details: Ignition version 7.9.7