The bug

When a parsing exception inside a nested command occurs the command returns that it ran unsuccessful, however it still gets executed.

How to reproduce

Use the following command and place a comparator next the command block or a conditional chain command block with a command

/setblock ~ ~1 ~ oak_sign{Text1:"\"Q\"",Text2:"\"Q\"",Text3:"\"Q\"",Text4:"Not JSON!"}

The first JSON data for Text4 is invalid, but instead of not placing the sign at all or ignoring this, it places the sign but states it was unsuccessful