Oh I see now. This is the result of your TOP chain being in 16-bit float pixel format (this occurs inside the sharpen effect you are using). The 16-bit float gives you image pixel values ranging from -64000 to +64000.
The HSV Adjust TOP clamps values between 0-1, so it changes the data going into the Blur. HSV Adjust does this for a few reasons, but most other TOPs do not. Note the Level TOP’s first parameter is “Clamp to 0-1”, this has the same effect.
So the Blur TOP is indeed working and blurring with the HSV Adjust bypassed, but you can not ‘see’ the blur because viewers and your monitor are all 8-bit (okay, maybe you have a fancy 10-bit monitor, but its not common). You can see the blur at work in the Blur TOP if you make the ‘Viewer Active’ and turn on the Normalized Split viewing mode. This doesn’t change the data, it just normalizes the range of pixel values to 0-1 so you can see the effect here.
Another way to you can inspect the values on the pixels in your image is to attach a TOP to CHOP to your TOP of interest.
Hope that answers why it is happening, now the question is what effect you want to go with?!