I caught this just before it made a mess:
That container lives in the garage, where the air temperature pretty much tracks the weather.
When the air in the main compartment heats up, it pushes fluid up into the dispensing compartment. Although both caps were screwed on finger-tight, apparently the smaller cap leaks just enough that the pumped fluid can push the air out through the not-so-good seal.
Another few weeks and it’d be sitting in a puddle!