Eraser tool not functioning properly on shapes I've created

[hanaa76414654]

When I erase on a regular shapes such as a rectangle it erases normally. However, when I try to erase, it creates a new path and just messes up my work. In the first, I tried to erase a straight line. The second picture is the original, the third is after I tried to erase a straight line into the black when it's not 100% opaque.

[Jacob Bugge]

Hana,

I believe this explains, and maybe gives clues to best way.

Illustrator tool galleries

[Monika Gause · Accepted solution]

Please read this to understand the easer tool:

Mysteries of the Eraser Tool — Revealed! « Adobe Illustrator blog