Stray part on 105 shifter

Roy Sinnamond said:

I posted this a month or so ago but no one bit. Giving it another go...

So, I'm going down a hill the other day and apply a little front brake
going into a turn. I release the brake and get up from the saddle to
accelerate. Unfortunately, the brake is still engaged!

The lever was still "squeezed"(squozen?). A plastic part was wedged in the
mechanism.

In the following exploded diagram-

<http://bike.shimano.com/media/cycling/techdocs/en/bikecomponents/ST/EV-ST-5510_v2_m56577569830557305.pdf>

<http://tinyurl.com/c8ssg>

The part in question is number 7 "L.H. Rear cover".

I tried putting the part back in place but it seems prone to come loose
again. I really don't want involuntary front brake application so I left
it out. The braking and shifting works fine without it.

My question is should I care about this part?

What is it doing there anyway?

I think it's a safety doohicky to prevent the brake cable end from
sdomehow becoming dislodged...BUT if the lever works w/o it, leave it
out STI has all sorts of plastic pieces that sometimes do nuthin.

Quoted message said:

--
Roy Sinnamond
roysinnamond at mac dot com